[Samba] RPC error logging in to PDC on Win-64

[EA]

I've upgraded one of my client boxes to Windows 64 bit edition but now it cannot login to the Samba PDC, instead it gives a RPC error after entering the password. The Win32 boxes can still login fine.

I can get accounts without admin rights to login but those with the rights are given a message stating "The system cannot log you on due to the following error:
A remote procedure call (RPC) protocol error occurred.
Please try again or consult your system administrator.