Since this happens to one unlucky soul every month, I want to stick this with some basic info.
Short answer: Restart your computer and/or try another browser
Long answer: CSRF tokens are a means of web security in which our site give you a tiny token for when you submit a form back to us. If the token is missing or doesn't match, you can't post to the site. It prevents friends from sending you malicious URLs here that trick you into posting things you didn't intend. VBulletin, the software we run, has no fix that I've seen for this issue sans upgrading to the latest version and leaving behind many of the things we need to run the site (like reviews).