Hiya,
I didn't want to file a bug just yet, in case I'm doing something wrong. But a recent subsites module commit on 3/13/2010 seems to block logging into the admin area for me.
Line 254 in SiteTreeSubsites.php.
if(!$this->owner->SubsiteID) return false;
If I comment this out, then everything is fine otherwise I can only get to the public subsites and not the admin area. sharvey you out there? Just curious what I might be doing different from you.
Thanks,
Wilson