Sorry, I think I posted about this in the wrong forum, so this may seem redundant for any admins.
Either way, I’m also having this issue with my Avisio theme. I tried upgrading both WordPress 3.1.1 and Avisio 1.2 (I’ve downgraded back since I noticed it still wasn’t working, and wanted my theme edits to remain intact as the site is live).
I still keep getting the Error 404 page. Not sure what I’m supposed to do from here on.