The "Drive stop" message is caused when the computer shuts down the drive. This can be caused by 1) a faulty rudder
reference, 2) drive exceeding the preset stop limits, 3) the AP can not turn the rudder. The last can be caused by a bad drive, bad steering parts
, excessive weather helm
If your rudder indicator is 3-5 degrees off, it would cause the AP to think that is has exceeded it's pre set rudder limits earlier than it should. It would also let the rudder travel too far on the opposite side. You can center the rudder display in the set up program.