The shaft/jackscrew is stripped and/or as well as the 'housing'. Unplug the unit and take a look inside. You didn't say how old it is, but if it's gotten a lot of use, it may be a simple matter of replacing the stripped parts. Look for shavings and such.
Maybe others have a thought. (Maybe not since Genie isn't a Sears opener. Just kidding!) My best to ya and hope this helps.