Is it bad media or compatability I'm dealing with?

I produced 17 DVDs with a Panasonic DMR-E20. Then, 11 of them froze up while playing on a Sharp DV-N55 home DVD machine. All are 2 hours long, recorded at 2 hour quality level. Some played for 30 minutes, others up to nearly 2 hours, and didn't have a problem until, they simply froze on a scene. This was repeatable says the client.

In two other machines, one a Sony, one a Panasonic, these discs are playing flawlessly and when repeated, are playing right past the points where the Sharp player froze.

Prior to this problem, I have produced 32 DVD-Rs, all of which went to 24 individual clients. Each has reported no problems and the media has remained the same. I'm using a co-branded DVD-R from CompUSA.

I'm inclined to believe the player is simply marginally compatable and this will continue to happen. Can a player really be *marginally* compatable? Playing for an hour or so without problem, then simply freezeing up? Other than freezing in place, no other problems were reported by this client.

Feedback would be appreciated. Thank you!