I've split this into a new post, since it was unrelated to the previous thread on
running Ulead DVD Workshop 2 in Windows 7.
VTS = video title set.
Every video in a title set much have matching specs -- specifically resolution, frame rate, and available audio streams. (MPGE-2 bitrate isn't an issue for authoring.)
If you're ending up with a new VTS, it means that your project includes mismatched source files.
However, this is nothing to worry about. This is merely the way authoring must happen. There's no reason to worry. Don't try to force an asset to another spec simply to squeeze it into the same VTS.
Another reason for the VTS is because you've run out of files allows (9 total). However, since the max file size for a VTS is 0.99GB, that would mean you're making a VTS large than 9GB, and therefore not a DVD. Anything beyond the size of a DVD9 (DVD+R DL) is illegal to the specs. In fact, some authoring software refuses to even author above a dual-layer max output size.