XP Share access denied in Vista

I am having trouble accessing shares on a WINXP workstation

The XP workstation is using subnet 192.0.1.xxx and my Vista Client is on
subnet 192.168.10.xxx that is hosting the WIN2K3 Domain. THe XP Client FQDN
is the same as the WIN2K3 Domain (domain.local)

The subnets appear to be routing OK as I can access the shares using the IP
Address\sharename

The problem is that if I create a new SHARE on the XP workstation, and
restrict the permissions to a DOMAIN Account, (domain\username), I am not
able to access the share with the VISTA Client and get an Access Denied. If I
use another XP workstation, the resticted credentials work.

However, If I change the share permissions (and NTFS Permissions) to
EVERYONE (modify), the Vista Client is able to access the share and its
contents.

Disabling the IPv6 does not help. WTF

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Regards,

Joe Fenninger, MCSA
MS Small Business Specialist