I'm about to pull out what's left of my hair!
I've tried Nero 7, Nero 9, Roxio 10.2, and ImgBurn 2.5.0 to burn a 7.4 GB ISO to a DL disk.
I know the ISO is good, because I've mounted it as a soft volume before and used it extensively.
The PC is a Dell XPS 730, with a PLDS DH-16AS drive. Nero (both versions) said it burned OK, but the verify failed at the 50% point. Roxio burned a little more than half, and then it stopped with an error (and not much of a message: Sense: 03 ASC: 0C ASCQ: 00 (Command 2A)
The media is Memorex, but made by Ritek.
The log (I've manually changed/deleted some file names for security reasons):
I 17:21:37 ImgBurn Version 2.5.0.0 started!
I 17:21:37 Microsoft Windows Vista Ultimate Edition (6.0, Build 6001 : Service Pack 1)
I 17:21:37 Total Physical Memory: 3,142,276 KB - Available: 968,296 KB
W 17:21:37 Drive X:\ (FAT) might not support single files > 4 GB in size.
I 17:21:37 Initialising SPTI...
I 17:21:37 Searching for SCSI / ATAPI devices...
I 17:21:38 Found 1 DVD-ROM and 1 DVD
