today i have same trouble adding windows 7 machine to a samba domain thanks to samba ml i find this way,that work for me,

change registry key on windows 7 without changing anything on samba server

; Enable NT-Domain compatibility mode
; Default:
; [value not present]
; “DomainCompatibilityMode”=-

; Disable required DNS name resolution
; Default:
; [value not present]
; “DNSNameResolutionRequired”=-

; Disable requirement of signed communication
; My Samba works with signed communication enabled, so no need to disable it.
; Default:
; “RequireSignOrSeal”=dword:00000001
; Disable the usage of strong keys
; Default:
; “RequireStrongKey”=dword:00000001

; Enforce DNS suffix
“NV PrimaryDnsSuffix”=”domain.local”

remember to adact the damain.local to your local conf .

hope to helpfully