Token Expired?

[PTGigi]

Why do I get all the weird ones XD

So I was making a new thread and got this message when I clicked "Preview Message":

Your submission could not be processed because the token has expired.

Please push the back button and reload the previous window.

So what'd I do? Hit back *cross my fingers my work was saved* copy the text I'd written, refresh the page, notice my text was still there, then hit preview again. Same message.

So this time I just opened a new "New Thread" window and am working on my new thread in that (rather long tutorial of doom). When I hit preview in this new window it worked again.

So just wondering, what is this 'token' and what is the expiration limit?

While making my post I had to hibernate my computer twice. Neither time it did much except for this time.