Sounds strange... There could be many different things at fault here. How many bad Prodisc did you burn? If it's only a few it could still be remotely possible (but unlikely) that your spindle has some 'bad apples' and you're just unlucky enough to feed those bad ones to your 'bad' drive... Get a different spindle of the same media, clear learned media from QSuite, do a test burn with Nero CD/DVD Speed, and post the graph here.
Also, make sure you follow the basic burning principles: Don't multitask, make sure that memory/CPU-hungry appz (like antivirus) are not loaded when burning, use a relatively fast and defragmented drive for the files you're burning, and ensure and that the drive runs in UDMA2 mode. Try using a different IDE cable too, just in case.
If the problem remains, try reflashing in safe mode with an older firmware (BCDB or BCHB), clear learned media from QSuite, and try again.
What's the IDE setup of your drives? Are they chained together on the same IDE channel, or on seperate IDE channels? Are they chained with other devices? If they're together (or chained with another device) and the previous solutions didn't correct the problem, remove the other device and plug in the 'bad' drive on its own as master (remember to change the pin at the back of the drive to the master position if different, and if your mobo chipset is an older Via model make sure you don't connect your burner on the secondary IDE channel). Then clear the learned media and do a test burn with Nero CD/DVD Speed. If it still doesn't work, try installing the drive on another computer (again on its own as master) and test-burn again. Maybe posting a detailed Nero burn log would shed some light on the issue and more experienced users than myself could comment on it and offer advice.
That's all I can think of. If nothing works then you may have a gremlin inside your drive! If it's still under guarantee send it back, if not just stop using that media with it and swich to media that the drive can handle (like Verbatim). Good luck!