The only time that I have seen this message was when I responded to a post (quoting the relevant passage) and hit preview before adding my stuff. Quotes don’t count, apparently.
Seriously, I had the exact same experience mentioned above; I had tried to preview a post that had a quote in it – and nothing else. The system is designed to reject any posts that are just quotes and nothing else. . . it might be set so that you have to have more than the quote and “Me too.”
Apparently it’s a ploy of abuse on other boards. Our folks are better behaved . . . or perhaps they just hadn’t thought of trying that here . . . guaranteed to get them a mighty DopeSlap from our staffers if they do try.
When I was using IE, clicking the preview post button would occassionally insert random characters at the start of my typing. One such character was invisible, and seemed to trigger an “end of post” event. If that spurious character happened to be one of the first 3, or was it 8 back then?, the board rejected it with an error message.
I are stoopid. I had the whole thing in quotes, including my reply. How I didn’t realize that (I’ve only been posting to boards for 7 or so years, give me a break!) is beyond me.