login failures from XP 64 bit client

[Herb Lewis]

Running samba 3.6.6 (also tested with 3.6.15 though with a slight variation
of response there) that is joined to a Windows 2008 domain I get login 
failure
when I try to map a share from a XP 64 bit client. It also fails the 
same from
other clients that are also running version 5.2 of Windows OS. Works for
5.1 and 6.0 versions. Following link shows what version number applies to
different Windows operating systems.

http://msdn.microsoft.com/en-us/library/windows/desktop/ms724832%28v=vs.85%29.aspx

With 3.6.15 I was getting a slightly different response when I tried to map
the share by IP address versus by server name.

Any ideas where to look for the problem?
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