I’m following the wiki to try and setup SITL for the first time. MAVProxy doesn’t seem to open. I’ve included a couple screenshots of Cygwin and what happens when I try to open MAVProxy. Could anybody point me in the right direction?
That’s not a MAVProxy issue - the ArduPilot build is failing (the add_group error). There’s likely something wrong with your copy of the ArduPilot source code. Maybe try removing it and doing a git clone again?