I recently upgraded to mu 1.2.5a from 1.2.4 and now I have a similar problem. My overall site admin account works fine, but all other users cannot login from "/sites/wp-login.php". They can only login from "/sites/username/wp-login.php".
If they try to login from "/sites/wp-login.php" they get redirected to "/sites/wp-admin/profile.php" and the page fires a "You do not have sufficient permissions to access this page" warning.
I run ubuntu feisty, php5.x, apache2.x, and mysql5.x and I've never had this problem before upgrading to mu 1.2.5a. I'm not completely sure that the upgrade caused the error, because I run mu for a small school and no one complained until today, but it definitely worked fine for me at 1.2.4 and I really haven't done anything of note other than upgrading to 1.2.5a.
Anyone else have this problem? Anyone know how to solve it? I can't seem to find the answer in the forums.
Many thanks,
am