Hi everyone,
I got the same problem and finally figured out it was because of some of my assets file names that were causing glitches in the "AuthoredContent.xml" file.
Make sure the dvd project does not use any assets with filenames containing special characters that could interfere with xml coding. You may have to trash (or rename) auto-imported and/or transcoded files created by Encore inside the project's folder. If you trash them, Encore will ask you to locate the missing files when you next open the project. Simply relink to your original files after you've renamed them.
Good luck!