Looks like you missed one of the most mentioned items in this forum and in the documentation.
You forgot to turn off friendly HTTP errors in IE.
If you had you get the following error when logging in on your forum:-
Microsoft JET Database Engine error '80040e09'
Cannot update. Database or object is read-only.
/forum/login_user.asp, line 171
This means that you do not have permission to write to the database.
Permissions
require that they are changed directly on the server, contact your web
host to have the permissions changed, or see the following page if you
run the server yourself:-
http://www.webwiz.net/asp/faq/server_permissions.asp