It seems when I take a long time to read a thread and compose a message (say 15 minutes) in the post quick reply box I get this nonsensical error message after I push the post button:

Cantpost.JPG

I just log-in, read subscribed threads and respond and that get's me this message. The back button does not get me the text I wrote nor does it let me post any thing till I go back to the user control panel and reopen the thread.

FWIW I am using FireFox.