Yes, I had it all day yesterday. I could start a new topic, but not reply to my post at all.
After searching for people who had similar errors in other forums, it seemed it might have been my message being rejected - perhaps containing blacklisted words or a limit on posting links in a thread to stop spammers etc.
I split my reply into two separate posts, and rewrote the wording (not that there was anything offensive!) and it posted it ok.
Really not sure why it was blocking me, but rewording it appears to have worked