It comes and goes for various people, very strange. I did upgrade the message board software the night of 11/10/2011 which is just over a week ago. But no changes since. Like I said, the only thing I can suggest from this end is to clear cookies, and if that does not work, maybe you need more milk with those cookies.
I'll go do a search on the vBulletin support forum to see if anything pops up.

