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.