http://www.vbulletin.com/forum/showthread.php?t=195137
Basically, you must have used a 3rd party tool to do database maintenance/restoration at some point, because your tables are set to different language character sets. Ultimately you're going to need to make sure that your tables are set to the
latin1_general_ci collalation setting. One of them, somewhere (like maybe prefixset) is set to
latin1_swedish_ci by mistake.