Last competition I had a problem with our robot; I could turn both the controller and the cortex on and they would connect perfectly. After about 20 seconds of driving the robot would stop taking commands and repeat the last command given to it, ex. driving forward. Once this happens you lose control the robot. However, all three lights on the controller are still green. The only way to stop the robot is to shut the controller off. I use easyC, if that helps.
Things I have tried:
replace backup battery
swap from 2.0 keys to 1.0 keys.
degrade from firmware version 4.0
use different keys