If you find yourself unable to post, edit old posts, or edit the wiki after the forum update, try logging out and back in. The release notes mention a new single sign-on feature, and apparently the old login isn't invalidated- but neither does it have permissions to do anything.

You will need to do this for both the forum and wiki to regain access to both.

(The above is a player-based solution, so take with a grain of salt.)