I've never seen that message. I'm not too much of an expert on the forum system. It's a commercial product. However in this thread from April we showed you how to close the browser, return to the message you were replying to, and then use the Restore AutoSave button to get your work back. Oh, and did you try presing the back arrow like it says? Did you maybe see the Restore AutoSave button at that time? Did it work?

As far as why this might happen in the first place, it thinks you logged out and back in somehow in the middle of typing in a message. That would be something to do with the cookies in your browser. Since you are the only person to have reported this that I can remember, is it possible you have some sort of cookie nanny-safety system on your system that nukes cookies it's suspicious of or ?????