Samba4 'The account is not authorized to log in from this station' attempting to join domain

[steve]

Hi
alpha21-GIT-027f2b3

We can no longer join machines to the domain. I think this is a client 
issue. The machines come from a previous install and we have unjoined 
them by changing to workgroup and are now attempting to add them to a 
new domain.

Administrator can kinit fine and we are able to join Linux clients to 
the domain, just not windows.

This error persists also after setting:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters
enablesecuritysignature = 0x0
requiresecuritysignature = 0x0
and
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanworkstation\parameters
enablesecuritysignature = 0x0
requiresecuritysignature = 0x0

Both xp and win7 give the same error.

I looked in another post:

"This behavior can occur because the Local Group Policy, specifically 
those in the Computer Configuration\Windows Settings\Security 
Settings\Local Policies\Security Options folder have a restrictive setting."

But where do I find that on windows 7?

Any ideas?
Cheers,
Steve