When i go to myurl.com/admin which then redirects to myurl.com/Security/login and login correctly I get the message "You're now logged in as XXX" and a button "Login as somebody else" but I don't get the admin area anymore.

This started to happen when I moved the installation from a subdir to the root. Anything else works fine. For moving the site I moved all the files to the root, added setBaseDir("http://www.myurl.com/") in mysite/_config.php and changed the line "RewriteBase /subdir" to "RewriteBase /"in the .htaccess in the root dir. Did I forget anything?