What the OP didn't mention is the brand/model of the DVD drives the disc was tried in. Perhaps both PCs have the same brand/chipset of drive and there's an incompatibility. I found that 1 of the Voyager discs (season 6 disc 7 I think) wouldn't play right in an NEC 2500/2510 - two of the VOBs read corrupted (One was in the special features, and I think one was in an episode). Even tried on a fresh install of Windows and it still failed to play (AnyDVD or WinDVD) or rip successfully. That is, most of it played until it hit one of the VOBs that it couldn't read. My other DVD drives (ROM and writers) read it find, as did my standalone players.

I also seem to remember a ripguard or arccoss protected movie (not sure which movie but it was within the last 6 weeks) that many members could not get a backup on due to their NEC drives. Other members got the backup fine with other brands of drive.

So far, my 3520 has had no problems. When I first got it, I even tested it with the Enterprise disc that the 2500s didn't like. It had no problem. The 3520 even was able to read some discs that my Lite-On DVD-ROMs and 411@811 had problems reading. Do you have any specific examples of other titles that cause problems on NEC drives (particularly on a 3520)? If so, I'd like to see if I can find one to test...