This is too weird, just had the V3.1 plugged in and programed the 21.5 spec GT for less drag brake, then programmed my other one in my 17.5 TC. I then decided to reprogram the 21.5 and it won't connect to the programming box.

I'm wondering if I programmed something it didn't like......little help?!

May want to drop this over in the hobbywing offroad support thread - some of the staff members seem to monitor it.
http://www.rctech.net/forum/electric...-off-road.html

Did you try turning the plug around? They only work one way although its just as easy to plug in either way.