> I'm not sure of the cause, but next time you get the "Authorization Required" screen, take a look in your address bar and post what you see there. It might provide a clue as to what's happening.

Seconded, and may I add the following:

Don't put anything in those boxes. At all.

The message forum doesn't use passwords, so it must be something else asking you for it. And if something is asking for your password without properly announcing exactly who it is, it should be considered a warning sign. Have you scanned for spyware lately?

A quick solution would be to copy your post content before you submit it. That way, if it does all go pear shaped again and vanish into the ether, you can just paste it back in again.