David,
Is it time for me to order a new Duex5?
Thanks

David, the DueX I2C errors 20094 occurred after printing about eight layers of a 40x40 test cube. I cancelled the print and sent an M18 command, but the error remained. Here is a photo of my wiring. I am using 14 AWG silicon covered wires for the VIN terminals. I also tried another ribbon cable.

2:55:59 PMM122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.02beta1(RTOS) running on Duet WiFi 1.02 or later + DueX5
Board ID: 08DGM-956GU-DJMSJ-6J1FA-3SJ6J-TAQVF
Used output buffers: 1 of 20 (18 max)
=== RTOS ===
Static ram: 28476
Dynamic ram: 98316 of which 0 recycled
Exception stack ram used: 484
Never used ram: 3796
Tasks: NETWORK(ready,400) HEAT(blocked,1192) MAIN(running,1660)
Owned mutexes:
=== Platform ===
Last reset 00:21:44 ago, cause: power up
Last software reset at 2018-08-20 17:31, reason: User, spinning module GCodes, available RAM 3740 bytes (slot 0)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0441f000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 10
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 0.0ms, max retries 0
MCU temperature: min 36.4, current 36.5, max 36.9
Supply voltage: min 24.4, current 24.5, max 24.7, under voltage events: 0, over voltage events: 0
Driver 0: standstill, SG min/max not available
Driver 1: standstill, SG min/max not available
Driver 2: standstill, SG min/max not available
Driver 3: standstill, SG min/max not available
Driver 4: standstill, SG min/max not available
Driver 5: standstill, SG min/max not available
Driver 6: standstill, SG min/max not available
Driver 7: standstill, SG min/max not available
Driver 8: standstill, SG min/max not available
Driver 9: standstill, SG min/max not available
Expansion motor(s) stall indication: yes
Date/time: 2018-08-21 14:55:58
Slowest loop: 180.64ms; fastest: 97.54ms
=== Move ===
Hiccups: 0, StepErrors: 0, LaErrors: 0, FreeDm: 240, MinFreeDm: 240, MaxWait: 0ms, Underruns: 0, 0
Scheduled moves: 0, completed moves: 0
Bed compensation in use: none
Bed probe heights: -0.015 -0.010 -0.012 0.000 0.000
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1
Heater 0 is on, I-accum = 0.0
Heater 1 is on, I-accum = 0.4
=== GCodes ===
Segments left: 0
Stack records: 2 allocated, 0 in use
Movement lock held by null
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is ready with "M408 S0 R50" in state(s) 0
daemon is idle in state(s) 0
queue is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 196.77ms; fastest: 0.08ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8

• WiFi -
  Network state is running
  WiFi module is connected to access point
  Failed messages: pending 0, notready 0, noresp 0
  WiFi firmware version 1.21RC4(08b3)
  WiFi MAC address 60:01:94:73:54:18
  WiFi Vcc 3.37, reset reason Turned on by main processor
  WiFi flash size 4194304, free heap 15752
  WiFi IP address 192.168.86.30
  WiFi signal strength -51dBm, reconnections 0, sleep mode modem
  Socket states: 0 0 0 0 0 0 0 0
  === Expansion ===
  DueX I2C errors 20094

Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
Firmware Electronics: Duet WiFi 1.02 or later + DueX5
Firmware Version: 2.02beta1(RTOS) (2018-08-12b5)
WiFi Server Version: 1.21RC4(08b3)
Web Interface Version: 1.22.1

Unfortunately my latest M122 contains "DueX I2C errors 9602"

7:42:48 PMM122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.02beta1(RTOS) running on Duet WiFi 1.02 or later + DueX5
Board ID: 08DGM-956GU-DJMSJ-6J1FA-3SJ6J-TAQVF
Used output buffers: 1 of 20 (14 max)
=== RTOS ===
Static ram: 28476
Dynamic ram: 98316 of which 0 recycled
Exception stack ram used: 460
Never used ram: 3820
Tasks: NETWORK(ready,400) HEAT(blocked,1192) MAIN(running,3476)
Owned mutexes:
=== Platform ===
Last reset 00:03:56 ago, cause: power up
Last software reset at 2018-08-20 17:31, reason: User, spinning module GCodes, available RAM 3740 bytes (slot 0)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0441f000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 10
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 0.0ms, max retries 0
MCU temperature: min 26.9, current 32.8, max 33.0
Supply voltage: min 24.4, current 24.5, max 24.7, under voltage events: 0, over voltage events: 0
Driver 0: standstill, SG min/max 0/1023
Driver 1: standstill, SG min/max 0/1023
Driver 2: standstill, SG min/max 0/0
Driver 3: standstill, SG min/max not available
Driver 4: standstill, SG min/max not available
Driver 5: standstill, SG min/max 65/219
Driver 6: standstill, SG min/max 59/202
Driver 7: standstill, SG min/max 65/200
Driver 8: standstill, SG min/max not available
Driver 9: standstill, SG min/max not available
Expansion motor(s) stall indication: yes
Date/time: 2018-08-20 19:42:47
Slowest loop: 180.60ms; fastest: 3.09ms
=== Move ===
Hiccups: 0, StepErrors: 0, LaErrors: 0, FreeDm: 240, MinFreeDm: 236, MaxWait: 14990ms, Underruns: 0, 0
Scheduled moves: 24, completed moves: 24
Bed compensation in use: none
Bed probe heights: 5.000 5.000 5.000 0.000 0.000
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1
Heater 0 is on, I-accum = 0.0
Heater 1 is on, I-accum = 0.3
=== GCodes ===
Segments left: 0
Stack records: 2 allocated, 0 in use
Movement lock held by null
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is ready with "M408 S0 R11" in state(s) 0
daemon is idle in state(s) 0
queue is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 196.78ms; fastest: 0.01ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8

• WiFi -
  Network state is running
  WiFi module is connected to access point
  Failed messages: pending 0, notready 0, noresp 0
  WiFi firmware version 1.21RC4(08b3)
  WiFi MAC address 60:01:94:73:54:18
  WiFi Vcc 3.37, reset reason Turned on by main processor
  WiFi flash size 4194304, free heap 15672
  WiFi IP address 192.168.86.30
  WiFi signal strength -53dBm, reconnections 0, sleep mode modem
  Socket states: 0 0 0 0 0 0 0 0
  === Expansion ===
  DueX I2C errors 9602

Thank you David. I will give it a try.

David,
Does my DueX I2C errors 2462 mean my DueX 5 board is dead?
Thanks

Here are the before and after M122 reports.
After has a "DueX I2C errors 2462"

11:16:36 PM
M122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.01(RTOS) running on Duet WiFi 1.02 or later + DueX5
Board ID: 08DGM-956GU-DJMSJ-6J1FA-3SJ6J-TAQVF
Used output buffers: 1 of 20 (9 max)
=== RTOS ===
Static ram: 28476
Dynamic ram: 96240 of which 16 recycled
Exception stack ram used: 320
Never used ram: 6020
Tasks: NETWORK(ready,400) HEAT(blocked,1192) MAIN(running,3540)
Owned mutexes:
=== Platform ===
Last reset 00:01:17 ago, cause: reset button or watchdog
Last software reset at 2018-08-17 17:19, reason: User, spinning module GCodes, available RAM 5976 bytes (slot 3)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0041f000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 10
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 0.0ms, max retries 0
MCU temperature: min 28.8, current 31.3, max 31.6
Supply voltage: min 24.4, current 24.5, max 24.8, under voltage events: 0, over voltage events: 0
Driver 0: standstill, SG min/max not available
Driver 1: standstill, SG min/max not available
Driver 2: standstill, SG min/max not available
Driver 3: standstill, SG min/max not available
Driver 4: standstill, SG min/max not available
Driver 5: standstill, SG min/max not available
Driver 6: standstill, SG min/max not available
Driver 7: standstill, SG min/max not available
Driver 8: standstill, SG min/max not available
Driver 9: standstill, SG min/max not available
Expansion motor(s) stall indication: no
Date/time: 2018-08-18 23:16:35
Slowest loop: 28.78ms; fastest: 2.96ms
=== Move ===
Hiccups: 0, StepErrors: 0, LaErrors: 0, FreeDm: 240, MinFreeDm: 240, MaxWait: 0ms, Underruns: 0, 0
Scheduled moves: 0, completed moves: 0
Bed compensation in use: none
Bed probe heights: 0.000 0.000 0.000 0.000 0.000
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1
Heater 1 is on, I-accum = 0.0
=== GCodes ===
Segments left: 0
Stack records: 1 allocated, 0 in use
Movement lock held by null
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is idle in state(s) 0
daemon is idle in state(s) 0
queue is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 16.05ms; fastest: 0.01ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8

• WiFi -
  Network state is running
  WiFi module is connected to access point
  Failed messages: pending 0, notready 0, noresp 0
  WiFi firmware version 1.21RC4(08b3)
  WiFi MAC address 60:01:94:73:54:18
  WiFi Vcc 3.37, reset reason Turned on by main processor
  WiFi flash size 4194304, free heap 17136

WiFi IP address 192.168.86.35
WiFi signal strength -49dBm, reconnections 0, sleep mode modem
Socket states: 0 0 0 0 0 0 0 0
=== Expansion ===
DueX I2C errors 0

11:18:25 PM
M122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.01(RTOS) running on Duet WiFi 1.02 or later + DueX5
Board ID: 08DGM-956GU-DJMSJ-6J1FA-3SJ6J-TAQVF
Used output buffers: 1 of 20 (16 max)
=== RTOS ===
Static ram: 28476
Dynamic ram: 96276 of which 16 recycled
Exception stack ram used: 484
Never used ram: 5820
Tasks: NETWORK(ready,400) HEAT(blocked,1192) MAIN(running,3540)
Owned mutexes:
=== Platform ===
Last reset 00:03:06 ago, cause: reset button or watchdog
Last software reset at 2018-08-17 17:19, reason: User, spinning module GCodes, available RAM 5976 bytes (slot 3)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0041f000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 9
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 0.0ms, max retries 0
MCU temperature: min 31.3, current 32.9, max 32.9
Supply voltage: min 24.4, current 24.5, max 24.7, under voltage events: 0, over voltage events: 0
Driver 0: standstill, SG min/max 0/214
Driver 1: standstill, SG min/max 0/124
Driver 2: standstill, SG min/max 0/0
Driver 3: standstill, SG min/max not available
Driver 4: standstill, SG min/max not available
Driver 5: standstill, SG min/max 48/240
Driver 6: standstill, SG min/max 43/229
Driver 7: standstill, SG min/max 51/241
Driver 8: standstill, SG min/max not available
Driver 9: standstill, SG min/max not available
Expansion motor(s) stall indication: yes
Date/time: 2018-08-18 23:18:24
Slowest loop: 232.36ms; fastest: 2.96ms
=== Move ===
Hiccups: 0, StepErrors: 0, LaErrors: 0, FreeDm: 240, MinFreeDm: 236, MaxWait: 122958ms, Underruns: 0, 0
Scheduled moves: 13, completed moves: 13
Bed compensation in use: none
Bed probe heights: 0.000 0.000 0.000 0.000 0.000
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1
Heater 1 is on, I-accum = 0.0
=== GCodes ===
Segments left: 0
Stack records: 2 allocated, 1 in use
Movement lock held by aux
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is idle in state(s) 0 5
daemon is idle in state(s) 0
queue is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 234.35ms; fastest: 0.08ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8

• WiFi -
  Network state is running
  WiFi module is connected to access point
  Failed messages: pending 0, notready 0, noresp 0
  WiFi firmware version 1.21RC4(08b3)
  WiFi MAC address 60:01:94:73:54:18
  WiFi Vcc 3.38, reset reason Turned on by main processor
  WiFi flash size 4194304, free heap 15672
  WiFi IP address 192.168.86.35
  WiFi signal strength -50dBm, reconnections 0, sleep mode modem
  Socket states: 0 0 0 0 0 0 0 0
  === Expansion ===
  DueX I2C errors 2462

i'll check tonight and will report back tomorrow.
Thanks again.

Thanks. I changed the wiring and I am still getting the same error. I am going to take my Duetwifi from my DC42 Delta and will try it on my CoreXY, and visa versa.

Thanks for the response David. I am using a 24V 20A 500W Max power supply and have separate wires (14 AWP silicon) from the power supply to the Duet Wifi and Duex5. Should I also have a ground wire connecting the two negative VIN terminal blocks (Duet Wifi & DueX5)?

My printer: CoreXY - Three Z Stepper Motors
Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
Firmware Electronics: Duet WiFi 1.02 or later + DueX5
Firmware Version: 2.01(RTOS) (2018-07-26b2)
WiFi Server Version: 1.21RC4(08b3)
Web Interface Version: 1.21-RC4
VIN 24.5V, BLTouch, 0.9 Steppers for all axes, 1.8 for extruder
E3D V6 with Bondtech BMG extruder

Problem is when the Duet is running for at least five minutes, the print stops and starts, like its buffering. I slowed the print down to a crawl and this behavior continues, less than 10 mm/s. The MCU temp is below 50 when this happens. I calibrated the MCU temp at room temperature and included the adjustment in my config.g. I tried changing SD cards, but that did not help. I hope it's a small issue with my config!
Thanks for your help.

Here is my config.g

; Configuration file for My Printer
; Communication and general
M111 S0 ; Debug off
M550 PRailCore300ZL ; Machine name and Netbios name (can be anything you like)
;*** If you have more than one Duet on your network, they must all have different MAC addresses, so change the last digits
M540 P0xBE:0xEF:0xDE:0xAD:0xFE:0xEE ; MAC Address

;*** Wifi Networking
M552 S1 ; Turn network on
M552 P192.168.86.239 ; Machine IP address
M555 P2 ; Set output to look like Marlin
M575 P1 B57600 S1 ; Comms parameters for PanelDue

G21 ; Work in millimetres
G90 ; Send absolute coordinates...
M83 ; ...but relative extruder moves

; Axis and motor configuration
M584 Z5:6:7 ; Z steppers are 5 (front left) 6(rear left) 7(right) on the duex5
M667 S1 ; CoreXY mode
M569 P0 S0 ; Drive 0 goes forwards (change to S0 to reverse it)
M569 P1 S1 ; Drive 1 goes backwards
M569 P2 S1 ; Drive 2 goes forwards
M569 P3 S0 ; Drive 3 goes forwards
M569 P4 S0 ; Drive 4 goes forwards
M569 P5 S0 ; Drive 5 goes backwards
M569 P6 S0 ; Drive 6 goes backwards
M569 P7 S0 ; Drive 7 goes backwards

;Leadscrew locations
M671 X-36:-36:293 Y20:276:147 S7.5 ;Front left, Rear Left, Right S7.5 is the max correction - measure your own offsets, to the bolt for the yoke of each leadscrew

M350 X16 Y16 Z16 E16 I1 ; set 16x microstepping for axes& extruder, with interpolation
M574 X1 Y1 Z0 S0 ; set homing switch configuration (x,y at min, z at max)
M906 X1000 Y1000 Z1000 E700:700:1000:1000:1000:1000:1000:1000:1000 I60 ; Per Kraegar's email
;M906 X900 Y900 Z900 E700 I60 ; Set motor currents (mA)
M201 X3000 Y3000 Z20 E1000 ; Accelerations (mm/s^2)
M203 X24000 Y24000 Z900 E3600 ; Maximum speeds (mm/min)
M566 X1000 Y1000 Z30 E20 ; Maximum jerk speeds mm/minute
M208 X260 Y280 Z300 ; set axis maxima and high homing switch positions (adjust to suit your machine)
M208 X0 Y0 Z-0.5 S1 ; set axis minima and low homing switch positions (adjust to make X=0 and Y=0 the edges of the bed)
M92 X201.5 Y201.5 Z1600 E415 ; steps/mm, X/Y may be more around 201.5 for accuracy

; Thermistors
M305 P0 T100000 B4240 R4700 H0 L0 ; Put your own H and/or L values here to set the bed thermistor ADC correction
;M305 P1 T100000 B4240 R4700 H0 L0 ; Put your own H and/or L values here to set the first nozzle thermistor ADC correction
M305 P1 X200 ; Use PT100 thermistor

M307 H1 A478.2 C213.6 D3.8 S1.00 V24.5 B0 ; Heater 1 model
M570 S360 ; Hot end may be a little slow to heat up so allow it 180 seconds
M143 S285

; Fans
M106 P0 H-1 ; disable thermostatic mode for fan 0
M106 P1 H-1 ; disable thermostatic mode for fan 1
M106 P2 H-1
M106 P0 S0 ; turn off fans
M106 P1 S0
M106 P2 S0

; Tool definitions
M563 P0 D0 H1 ; Define tool 0
G10 P0 S0 R0 ; Set tool 0 operating and standby temperatures
;*** If you have a single-nozzle build, comment the next 2 lines
;M563 P1 D1 H2 ; Define tool 1
;G10 P1 S0 R0 X0 Y17 ; Set tool 1 operating and standby temperatures

; Z probe and compensation definition
;*** If you have a switch instead of an IR probe, change P1 to P4 in the following M558 command
;M558 P4 X0 Y0 Z1 ; Z probe is an IR probe and is not used for homing any axes
;G31 X0 Y30 Z2.00 P500 ; Set the zprobe height and threshold (put your own values here)

;BLTouch - leave commented out if using a IR Probe
M307 H7 A-1 C-1 D-1
M558 P9 X0 Y0 Z1 H5 F50 T6000 A5 S0.02

G31 X2 Y42 Z2.66 P25 ; Customize your offsets appropriately.

M912 P0 S-3.5 ; Adjusts CPU Temperature readout

;*** If you are using axis compensation, put the figures in the following command
;M556 S78 X0 Y0 Z0 ; Axis compensation here

M208 S1 Z-0.2 ; set minimum Z
;
T0 ; select first hot end

;M501