What I presume was an earlier form of Macrovision used to drive me nuts with rental tapes. (This was back in the days of a simple RF connection to the tv.) Used to happen most often with CBS/Fox titles. I would return the tape to the rental store and complain it was impossible to watch the movie, and they would pop it into their machine and it played back fine! Either it was really incompatible with several makes of VHS machines, or the sneaky bastards had a video stabalizer in their store setup.