Finally narrowed my problems down! It's CopyToDVD.

DVDs I have written with CopyToDVD will not play in my stand alone player(s), but will play in my XBox.

Attempting to open a DVD-R created with CopyToDVD in DVDShrink results in an "Invalid Navigation Structure" error.

I was using an older version. I tried installing the latest version, but the problem remains.

Help!