Alright, I did some small modifications to the forum, I do hope this will fix most of the "Error 500" problems.
Basically you won't see the change, and that's the point, but now the message posting is compiled instead of interpreted (for those who knows about that) so it's technically more stable.
If you see any problem, let me know.
One other thing, which was a request from Sébastien, now when you quote, you won't see the author's signature. This will affect only new messages from now on, old message will do the same.
This applies that if you change your signature, ALL your old messages will have that new signature, so keep that in mind when you'll change it.
If you really think the Signature should be "per message" instead of "per user", we can always debate of this.
Next step will be the improvement of the "new messages" verification at the begining.. this is based on your last logon's date, and not the last message you checked or only messages you checked.. it might take a little longer to fix that, but please be patient.
Otherwise, all suggestions are welcomed!