Had a strange error message on one of the sites I manage. It said "Fatal error: Call to undefined function: pn_dbmsgerror()". This is a Post Nuke CMS system and the error occurred after a reboot to the physical server and we made some space on a partition that had filled up.
Turned out the problem was a corrupted table in the Post Nuke database. The table _referer got twisted and didn't know what it wanted to do with itself. This table is only used for tracking where people come from who visit your site, so since I had a back up of the database, I just nuked the table and copied over the table from the back up database. That got everything up and running again perfectly.