Wilf,

It's not you.  This is an intermittent problem that has been happening recently.  I can't seem to track it down and the Earthlink tech support has not been much help.  You are doing right to select the auto copy to clipboard.  Then you can paste the message back in if the post fails.  (cntrl/V)

To make double sure you can also manually copy the message (cntrl/C) before you preview or post.

It used to auto copy with out having to select it, but when IE7 came out we had to modify the forums to get rid of the stupid IE7 security warning:

http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1168054526

If you had the box checked when you hit post, then the contents of your message should not be lost.  It's probably still in the Windows clipboard unless you copied something else or shut down.  Post again and cntrl/V in the message box to see.