I have the same problem on Windows 7x64 running under normal user (non-admin) privileges. No error message comes up. My computer just sits there looking for credential tiles. I have let it run a long long time. I have to do ctrl-alt-del and then cancel to
get the computer back. Once it comes back I cant do anything anymore that requires privilege escalation and I have to reboot.
It seems that it only happens to me after using the dialog to elevate privileges and I don't hit the return key after entering the admin password. I can't say with certainty that this is the trigger. It might just be a perception.
I have an HP Pavilion dv6 laptop and I use the fingrprint reader to log in at startup but generally type in the admin password for privilege authentication. After this problem occurs the fingerprint system won't run either.