Upgrading 1.2 to 1.5 - no admin or settings accessible

hi guys

i have trouble while upgrading. i took a copy from the db of my live site. than i uploaded the 1.5 files to http://test.divexit.de .  changed the url in the table to the new url. and ran upgrade.php


So now at the first view everything looks like it works but i am not able to go to the admin page or setting. even changes on the dashboard are impossible.


i also commented out the line in .htaccess dave posted somewhere in here

Header append Vary User-Agent env=!dont-vary


at the moment i don´t know what should be my next step


thx for any help tipps or thoughts :-)