I'm also getting this problem.
Theme: Army by Skaidondesigns
Any and all MODs: None
Do you use a port of phpBB: 80
Version of phpBB: 2.0.21
Version of PHP: 4.4.6
Which database server and version: MySql 4.1.22-standard
Host: localhost or if you mean url address
http://bfk.clanservers.com/bfkgaming/forum
Did someone install this for you/who: Installed via the script library on cpanel on gameservers webspace
Is this an upgrade/from what to what: No
Is this a conversion/from what to what: No
Have you searched for your problem: Yes
If so, what terms did you try: Login Twice
State the nature of your problem: Having to login twice
Do you have a test account for us: no
Current cookie settings in admin control panal:
Cookie domain: Blank (nothing set)
Cookie name: phpbb2mysql
Cookie path: / (forward slash)