Sorry for bumping an old thread, but I'm having the exact same issue.
Webmaster tools shows a ton of soft 404s, and when I try and go to the pages I'm seeing the same as thing as the OP. The specified thread does not exist message.
--------------- Added [DATE]1388441097[/DATE] at [TIME]1388441097[/TIME] ---------------
Wow, the more I read up on this and see it's a known issue that VB has pretty said they don't care about or going to try and fix.
http://www.vbulletin.com/forum/forum...=1388426505040
http://www.vbulletin.com/forum/forum...b-master-tools
their official response is to check with vb.org if you want it fixed. Does anyone have any solutions to this?
Shouldn't the correct header be a 410 gone?