I am having the same issue. After I install, I login as admin, and go to ACP, and type in -http://forum.ingilizce.com/phpbb_seo/phpbb_seo_install.php
I am asked to login. I login, and then no matter what I clicked on, it asks me to login again. I tried bith IE and Firefox and no difference. The installation was on a new 3.0.6, with no other mods installed. I moved all the installation files but the congig file and the install folder.
The forum is on forum.ingilizce.com
Any ideas why this could be happening?