There seems to be something off with the structure of the dvd. One thing you might try is to run the dvd on the hard drive through FixVTS. http://www.videohelp.com/tools/FixVTS
No guarantee that it will work, but it is one thing to try at least.
Another possibility is to reauthor the vob files into a new dvd. You would lose extras and the original menu when doing this. My normal process for doing this is to take the video out of the original vob files and make an mpeg2 file with them, using Vob2Mpeg. This is a free tool, and doesn’t degrade the quality of the video.
Then import the mpeg2 file you just made into AVStoDVD. Since the video and audio will already be compliant to dvd specifications, it will simply pass them through and build a new dvd for you, with or without a menu, depending on what you want. AVStoDVD is also free. Just make sure to set it up to make a dvd that fits your area. In the US, we use NTSC dvds. Most of the rest of the world uses PAL specifications.
If that sounds too complicated, try a different dvd decryption program. You can get a trial copy of DVDFab. Use the DVD Copy section of that program. It also has a free section that will continue to work as a decrypter/ripper after the trial ends. That free section is called DVDFab HD Decrypter.