i have gotten this a few times. when submitting a post, and making a new thread. one time, i got this when i was making a new thread, then i pressed [Yes, I Agree] and then it took me to a blank page, and my thread was gone.
it seems this happens whenever dave does maintenance.
-Happened to you when he was adding a new plugin
-Happened to me right after he rolled back the server two hours.