Before I left on my business trip, I took a quick look at this problem. The file system was intact, the action segment, route classes, content tables were populated. His admin permissions were slightly askew (which was odd). I believe he has some slight data corruption in the CMS which needs to be pin-pointed.
If it was me I would be logging that error-position to discover who invoked it with what data. Something I could not due with the trace-back given and the short amount of time I had available.
I would suggest, he hire someone to track this down programmatically and fix the corruption. The problem is beyond the kind of assistance we can give verbally, in my opinion.
PS: I could fix it for you, but you would have to pass me a copy of your database. Solving this kind of problem remotely would require too much of my time.