For some reason my backup stalls between 75 and 83 percent.  I have tried running the full database repair, but don't know what else to try.  Any suggestions?

First of all, let's rule out unlikely but easily verifiable external problems:
- Have you tried rebooting your PC and trying the backup again?
- Have you made sure that it's not a case of out of memory or disk full?
If the answers to those two questions are Yes, as I assume, then we most likely have a data problem. Database repair fixes most, but not all such problems.

So I would suggest trying to export your collection. Does that work? If it does, try loading the exported XML file in some program. I favor XML Notepad, but Firefox works fine, too. Both will spot illegal data in an XML file and give you a line number.

Given a line number, you need to open the XML file in a text editor that shows line numbers. Plain old Notepad will not do. My favorite text editors are Editpad Lite and Notepad ++ (both freeware). Both of those will load large files quickly and let you go to the offending line. From there you have to find out what the profile is that contains the error. Then remove that profile from your collection and try the export again.

If the above doesn't solve the problem, I have some other suggestions, but let's start with this.

EDIT: I just saw your post in Plugins. You might want to try unloading LoadDVDPro before running the backup. Or in fact unload all plugins that you are using.