WordPress MU

Hello,
I have the latest version of wordpress installed(2.6.3) and when I try to login after registering a normal account and creating a blog, and verifying account, and receiving a password, It just reloads the login page. Login in as the admin of the MU system works fine, but for some reason registered users can not.

What error they get? Invalid password or nothing?

I had this problem too after I upgraded to revision 1518. It turned out that following extra lines in wp-config.php, which weren't there in wpmu 2.6.3, caused the problem:
define('DOMAIN_CURRENT_SITE', 'current_site_domain' );
define('PATH_CURRENT_SITE', 'current_site_path' );

Deleting those lines fixed it.