6.6.0.0 "There was an error adding your device" on 64s with 5.0 FW

Call Garmin support for detailed help

Looks like it's time for me to find out where Express logs technical errors.. No thanks to the tier-1 indian support system that will basically tell me to do what I said I did in OP. Seems this forum is totally worthless..

Too many areas that could be wrong here within your system, I've always had good support when calling Product Support so it's your best bet. You could try going back to an earlier restore point, it's not unknown for a Windows update to break stuff.

I uninstalled, then pasted this in a .bat and ran as admin and rebooted.. Fixed

Detailed logs are in \ProgramData\Garmin\Logs\ but I didn't bother analyzing mine I just cleaned and planned to do so if wiping didn't work

rmdir /S /Q "C:\ProgramData\Garmin\"
rmdir /S /Q "C:\Program Files (x86)\Garmin"
rmdir /S /Q "C:\Users\*\AppData\Local\Garmin_Ltd._or_its_subsid"
rmdir /S /Q "C:\Users\*\AppData\Local\Garmin\"
rmdir /S /Q "C:\Users\*\AppData\Local\Temp\*Garmin*"
rmdir /S /Q "C:\Users\*\AppData\Roaming\Garmin\"
del /f /q "C:\Users\*\AppData\Local\Temp\*Garmin*"