I just began an upgrade from 2.8.6 to 2.9.2. File uploads were fine, although I forgot to keep the wp-config.php file from the 2.8.6 installation. So that was recreated without hassle. I was then told I could log in, so I did. My credentials were still in the database, so I had to log in with those, which was fine on the front end. But when I try to access the wp-admin area, my browser keeps trying to redirect me in an endless loop now.
What could be causing that?