It all comes down to your drive not being able to handle the media. And from what you say this same drive/media combo has no problem burning if in your old system....could you post a log from there?
Even with bitsetting your players don't like the +R?
NVM..I just reread what you wrote, you are using a standalone DVD recorder. I've heard they are trickier to satisfy than simply a DVD player.
It sounds like a problem with your standalone player recognizing the files since Vista sees them and plays them with no problems. Imgburn doesn't altar the files at all...it simply burns whatever you throw at it.