I have a Sansui vcr/dvd

Question

I have a Sansui vcr/dvd recorder combination. I've had it for a couple of years. DVD's that I have previously played on this unit now yield the error "Incorrect disc - error c104. I understand that the unit only play selected formats but these are discs that have previously played without a problem. Has the unit gone bad or is there something that I can do. Thanks.........