I have seen burners where the laser output falls off and they no longer burn reliably - can be as simple as a little dirt on the lens...

In this instance I think a good guess might be that the printable disks require a little more energy in the laser to get a good burn than the non-printable ones and that your burner has dropped below this threshold.

Given that you "burn 100's of CDs" it may simply be that the laser LED has deteriorated.


--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!