Thats Right, This is from Wayne Luke over at the VBulletin.com site
All tables and fields should be the same collation to prevent this error from occuring in the future. It can occur on other queries not just when upgrading if there are mixed collations. When vBulletin creates new tables and fields it will use the default of the database for the collation. This is usually latin1_general_ci unless you change it. You can see instructions on how to change a database's collation settings in the MySQL manual.