As you are on 1.21RC1 you may need to follow the procedure for updating from 1.20 to 1.21 or later. See https://duet3d.dozuki.com/Wiki/Installing_and_Updating_Firmware#Section_Upgrading_a_Duet_2_WiFi_or_Ethernet_to_firmware_1_21_or_later_from_1_20_or_earlier.
