@mark & sinner:

i don't run a board myself but i think you should be able to modify the PHP code in phpBB. provided below is a link to a PHP code that handles user logins/logouts and session expirations, caches etc.

php login script:
http://martin.f2o.org/download/php-l...cript/user.php
http://martin.f2o.org/php/login-script-faq (the FAQ for above)

check that and compare with the one you got now!