I think 'forum error' occurs when someone else posts in the thread you're replying in, whilst you're typing your post.
I've generally got round this by clicking 'back' and my post is usually still there (the odd time it's not). Then, as NMA says, copy the text, refresh, paste and post (if refreshing doesn't work, go back to the thread, click 'reply' to reopen a dialogue box, paste your text and post.
Originally Posted by: Saint Snow