cannot logout of wordpress after facebook connect

I am using facebook connect to let users register to the website and login. The logging in goes great but users connected through facebook cannot logout of the website…

I found this post:
http://stackoverflow.com/questions/2395292/log-out-of-both-wordpress-facebook

But it’s not working for me, maybe i did something wrong. I created fb_logout.php on the root of my domain, containing:

<?php
session_destroy();
header('Location: http://picturepalace.eu); ?>

Then in my theme i used:
<a href="#" onclick="FB.Connect.logoutAndRedirect('http://picturepalace.eu/fb_logout.php')">Sign out</a>

Any ideas on how to make the logout function work properly?