Dick,
You could have a failed roller per Ed's response or it could be a gear slipping/failed on the drive mechanism. It may be better to have Premier look at it if you don't have help to get the mattress out. If you have help, remove the mattress and see what your dealing with. Repair may not be too tough once you've diagnosed it and you can always run it up to Premier if needed. Give me a call if you have any questions, etc.
Steve