You may be seeing a problem with the current version of A500 ICS that appears to be caused by killing apps. Start by removing any task/app killing apps, removing any apps that force close, and avoid using the ICS App Manager to force close apps. You should be able to then clear the problem by using the pinhole reset switch to do a hard reset of the system (just press it with a paper clip while the system is on). The reset is only a temporary solution though if you still have apps being killed and/or force closed, so take care of that as soon as possible.
For details on the auto rotate issue you seem to be encountering, see the following tip on this site: 541508-possible-relief-several-a500-ics-related-symptoms-problems.html