Same issue here. All of a sudden. Changed to twenty-eleven and I can get in.
1. Deactivated plugins – didn’t work
2. Switched to 2011 – works
3. Re-ran upgrade via dashboard – works
4. Re-activated theme – doesn’t work
Also tried this:
1. Switched theme to 2011 works
2. Logged in
3. Switched theme back without logging out. Admin modules seem to be working just fine.
4. Tried to logout – freezes up
Seems to be something in the login.php hanging things up.
