I wanted to piggyback onto this as i have the same issue. (DuetWIFI coreXY build with IR probe, X and Y endstops are on high ends of build plate i.e 300, 290)

I was running 1.19 and was having connectivity issues to the webcontrol UI, but no issues with homing.

I updated just the other day to 1.20, and when i ran homeall, x and y homed, then z crashed to the bed.

So i recalibrated my z probe per the wordpress article, and the z probe was triggering as expected at the same value i had set before in G31. I tested G30 S-1, AND G30 both probed the bed and stopped before a crash.

My thought is that in the release notes there was mention of adding S2 to the M574 section, but doing that just caused the x and y to crash, never getting to Z.

Below is my config.g and homeall.g files, maybe someone can shed some light on this for me.

–---Config.g:-------

; Configuration file for testing Duet Ethernet and Wifi

; Communication and general
M111 S0 ; Debug off
M550 PHC300 ; Machine name and Netbios name (can be anything you like)
M551 Pcheats5 ; Machine password (used for FTP)
;*** 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:0xED ; MAC Address

;*** Networking - Enable for both WiFi and Ethernet boards.
M552 S1 ; Turn network on

;*** Ethernet networking: Adjust the IP address and gateway in the following 2 lines to suit your network
M552 P10.10.10.250 ; (0 = DHCP)
M554 P10.10.10.1 ; Gateway
M553 P255.255.255.0 ; Netmask

M555 P2 ; Set output to look like Marlin
G21 ; Work in millimetres
G90 ; Send absolute coordinates...
M83 ; ...but relative extruder moves

; Disable Fan 1 thermostatic mode
M106 P1 H-1

; Axis and motor configuration
M569 P0 S0 ; Drive 0 goes forwards
M569 P1 S0 ; Drive 1 goes forwards
M569 P2 S1 ; Drive 2 goes forwards
M569 P3 S1 ; Drive 3 goes forwards
M569 P4 S1 ; Drive 4 goes forwards
M574 X2 Y2 Z0 S0 ; set endstop configuration (all endstops at high end, active high)
;*** The homed height is deliberately set too high in the following - you will adjust it during calibration
M667 S1 ; switch to CoreXY mode
M208 X0 Y0 Z0 S1 ; Set axis minima
M208 X290 Y240 Z270 S0 ; Set axis maxima
M666 X0 Y0 Z0 ; put your endstop adjustments here, or let auto calibration find them
M350 X16 Y16 Z16 E16:16 I1 ; Set 16x microstepping with interpolation
M92 X80 Y80 Z400 ; Set axis steps/mm
M906 X500 Y500 Z500 E1120 I40 ; Set motor currents (mA) and increase idle current to 40%
M201 X1500 Y1500 Z1000 E1000 ; Accelerations (mm/s^2)
M203 X1000 Y1000 Z200 E3600 ; Maximum speeds (mm/min)
M566 X1200 Y1200 Z1200 E1200 ; Maximum instant speed changes mm/minute

; Thermistors
M305 P0 T100000 B3950 R4700 H30 L0 ; Put your own H and/or L values here to set the bed thermistor ADC correction
M305 P1 T100000 B3974 R4700 H30 L0 ; Put your own H and/or L values here to set first nozzle thermistor ADC correction
M305 P2 T100000 B3974 R4700 H30 L0 ; Put your own H and/or L values here to set 2nd nozzle thermistor ADC correction

M570 S180 ; Hot end may be a little slow to heat up so allow it 180 seconds

; Adjustments for J-heads used as dummy heaters on test rig
M307 H0 A250 C140 D5.5 B1
M307 H1 A250 C140 D5.5 B0
M307 H2 A250 C140 D5.5 B0

M557 X0:250 Y0:225 S25 ;mesh grid probe pattern

; Fans
M106 P1 S-1 ; disable thermostatic mode for fan 1

; 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 ; Set tool 1 operating and standby temperatures
M92 E837:837 ; Set extruder steps per mm
M143 H1 S290 ;set max hot end temp
M307 H1 A576.4 C196.8 D6 B0 S1 ;Set PID values for hot end
M143 H0 S125 ;set max bed temp
M307 H0 A146.6 C693.4 D9 B0 S1 ;Set PID values for Bed Heater

; 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 P1 X0 Y0 Z1 ; Z probe is an IR probe and is used for homing Z axis
G31 Z1.5 P500 ; Set the zprobe height and threshold (put your own values here)

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

;M208 S1 Z-1.95 ; set minimum Z

T0 ; select first hot end

-------Homeall.g–-------

G91 ; relative mode
G1 S1 X340 Y340 F3000 ; course home X or Y
G1 S1 X340 ; course home X
G1 S1 Y340 ; course home Y
G1 X-4 Y-4 F600 ; move away from the endstops
G1 S1 X10 ; fine home X
G1 S1 Y10 ; fine home Y
; Z homing section follows for IR Z probe
G1 X-30 F3000 ; X offset to get z probe to bed
G1 S1 Z-400 F500 ; course home Z
G1 Z2 F500 ; move away from the Z Probe
G1 S1 Z-4 F100 ; fine home Z
G90 ;back to absolute mode
G92 Z1.5 ;tell printer that it is at Z=1.5 (trigger height of z probe during homing)

It was a reversed endstop connector.

Silly me for assuming that the 3-pack of endstops would have all 3 sets of cable wired the same at the board connector One connector set was different than the other two which caused the issue.

I am also having the same problem. Windows 10 here. Doing first time setup.

I installed first using just the DueDriverFiles.zip then extracting.

When i double clicked the duet.inf file, it simply opened as a text document. So i righ clicked the duet.inf and selected "install" instead. It seemed to succeed (no errors were thrown). But when i then plugged the Duet Wifi into my USB port, no joy. The red LED is illuminated, but nothing shows on my PC. Device manager also shows no COM port objects.

I then read this post and downloaded the whole reprap firmware file from github. Then extracted the duetdriverfiles.zip again. Same thing, no errors (still had to right click and hit install rather than double click) but also still not showing up on device manager.

I have tried restarting my pc between attempts to install the driver as well for good measure.

I decided to try to uninstall the driver manually from my PC, so i found the file in Windows/System32/Driverstore/filerepository/duet.inf_amd64_78c3089bafb78e17 but the files could not be removed. The interesting thing about this is that the duet.inf and duetinf.cat files in this area were time stamped the same as the first driver file i tried to use. no other driver install attempt seems to have overwritten them.

Open to input on this. I had been following the steps laid out here: https://duet3d.com/wiki/Getting_connected_to_the_Duet_WiFi#Step-by-step_guide
got stopped at step 2-3.