Ah yes, the dreaded redirect error. Most likely was a problem with host config. I've had weird things like that happen to me as well, where using (or not using) the "www" can actually make a difference. Things like Host Records (A-Name vs C-Name and such) as well .htaccess can be tricky if not downright finicky. Presuming this has been fixed now?
I actually had to downgrade to an earlier version of vbulletin for my community forums because of this bug. I tried that same fix on my forum by adding www to the redirect, and that seemed to work for a day and then went right back to breaking again. If you guys find the answer, please do share . Otherwise, I'll be on the lookout too.
I absolutely love the new vb 4.0 features, and how user-friendly the admincp is now.