I can't seem to figure this one out. I have done tons of searching, read all the docs, checked the error logs, etc..

I am upgrading from 1.3.8a to 1.5.1. When I do an upgrade (using either my old configure.php files, modified and renamed dist-configure.php files, or modified configure.php files created by a clean install), I am unable to log in to admin. I get the login screen, the spinning wheel after entering my login info, and then a fresh login screen. I think I have ruled out id/password issues.

On the other hand, when I do an install with a new database, everything works fine.

I think I have tried enough variations to have ruled out any problems with configure.php. I also have used different browswers, cleared cache/cookies, etc. Because it works on a fresh install, it seems like the problem has to be with the upgraded database.

If I could just transfer over my customer and order data, I could live with rebuilding everything else.. but it seems like that would be a nightmare.

Any help would be greatly appreciated.