Look here: /Users/YOURACCOUNT/Documents/DVD Studio Pro Documents
If you see an AUDIO_TS folder and VIDEO_TS folder these are likely the ones that are being burned off rather than the project you expected.
To verify these are the culprits:
1. Drag the VIDEO_TS folder atop of DVD Player application and hit play.
If it's the the culprit delete this VIDEO_TS folder and the AUDIO_TS folder.
Why did this happen?
Well, it's likely that at some point you formatted and project and DVD Studio Pro dumped the files there, or DVD Studio unexpectedly quit sometime ago.
What if there are no folders there in DVD Studio Pro Documents?
1. Open DVD Studio Pro and hit COMMAND + (COMMA) to open it's preferences.
2. Click on "Encoding"
3. Select "Build/Format" next to the "Show:" menu.
4. The location shown for "Location" is likely where the problem VIDEO_TS and AUDIO_TS folders are.
5. Delete 'em.
6. Restart DVD Studio Pro and do a test burn. A simulation won't show you a problem, only a disk image or actual burned DVD will.
Some additional info:
Another way to check to see if DVDSP is pulling the wrong or old files is to hit COMMAND + F for Format. Look at what is shown in under the General tab under Disc and next to "Name:" and compare it to what is shown next to "Name:" in the Inspector palette; if they're different, then DVDSP is pulling old files from somewhere.
A clue that you've solved your problem is if you see this window appear when you hit COMMAND + F (for Format).