An error like that after running debug info usually indicates an incorrectly formatted users.txt file.
Now, it is possible the corruption occurred due to a players actual name using ascii characters that lua sees as code, we attempt to clean it up as much as possible, but, more often than not, it's due to manual editing of the file.
I believe our SVN is much better about anti-corruption than the release, which may be the problem (added user during old release?)
Please attach your servers data\ULib\ users.txt to the next post.
If you don't wish to show your users STEAM IDs (which for all intents and purposes, are public on servers anyway), please email it to teamulysses@ulyssesmod.net with the subject "Pantho: user info requested"
(It's much easier to just use the link at the bottom of your post that says "additional options" and attach the file.