Are there any reserved words that can't be used as category names? If I create a category called 'WP 6', then the link to display posts in that category on the website (say from the category widget), fails with an "Internal Server Error" page. Changing it to 'WP6' makes the links work fine. Seems to be all categories that have WP as a separate word in the category name.
OK OK, so I'm still running WPMU 2.6.3, don't shoot me down in flames. Regardless though, this is still irrational behaviour surely?!?