Yes, I thought it was just my system. I copy my post just in case but when I return to the main forum page my new post is there. Strange. This error code usually has something to do with SMTP authentication not being enabled but I'm not sure of its relevance unless our posts are treated as emails, which when you think about it, they probably are and we all share the same inbox and folders (such as General Discussion).
Modified P.S. funnily enough, it didn't happen with this post!