Have you tried rebooting the autopilot (i.e turn off and then on again)?
We had it happen to us that the autopilot did a doughnut (360 deg turn) in the middle of the gulfstream under sail at 25 kts of wind - a bit scary.
Once I got the boat under control the autopilot indicated that we were on a course of 90 deg while I was heading due west towards Florida.
M resourceful wife solved the problem by turning of the autopilot for 5 secs and then turning it on again. Worked a charm and never had problem since.
Also check for big pieces of metal objects that you may have placed close to the aitopilot compass unit...
Last edited by jorgenl; 10-03-2010 at 10:15 PM.