After about a year on the autopilot, I was flying last week, and the roll AP appeared to turn off with a roll error. After landing, I tried to check and test the AP. The Servo is seen on the network, the numbers change when I move the stick from + values to - values. I tried to do a test where it moves the stick automatically under test, but the selection on the screen will not allow me to select the test feature or the one above it. All that will work is the status screen. I am sure I can figure this out, but I need to be able to select the test feature. Any help here would be appreciated. The pitch servo works fine. I did nave a ground issue with the pitch servo power when I first installed the servo, but I think I corrected that. Would a poor ground cause this? Also why won't the screen select the TEST feature? Thanks.