I tried installing the current 2x beta client on my Vista Ultimate x64 at home, and after a reboot user login was not possible for any users (after entering the password it just popped back to the Fast User Switching screen). Booting to safe mode worked, and the errors in the event log referred to "loginui.dll failed in tuxcredprov.dll". Google gave no hits on the latter DLL, so I guess this is a new 2x component? I eventually had to do a repair installation of Vista to get back to normal operation.
