Another strange error message

I received this when I tried posting a reply to a thread:

The following errors occurred with your submission

Invalid Thread specified. If you followed a valid link, please notify the administrator.

I haven't come across this before, and haven't a clue what it means.

Pete

EDIT: this is the thread I was trying to respond to:

http://www.excelforum.com/excel-gene...isfortune.html

I see that Arlette had posted at (or just before) the time that I was trying to reply, so could that have something to do with it?