There are two possible names for the host-machine the server is on: www.groupdiy.com and just groupdiy.com. If the name you use on a specific session does not match your stored login cookie, you wind up going around a loop a few times.
I finally "fixed" it by deleting all my bookmarks to this place, making ONE bookmark, and always using it to visit.
ETHAN: Perhaps there is a tweak in the cookie handling so this doesn't happen? (I am so totally guessing.)