Windows 2003 File Share Issue

I have an issues with a domain controller and a fileshare.

Currently the setup is as follows.

D:\Shares\Test Share

Is shared and has Everyone set to Full Access

This can be accessed and works fine when a user is added to the the file permissions for read / write etc..

However when doing the following access is denied.

Remove UserA from the file permissions
Create a Group.
Add UserA to the group.
Add The Group for full access to the file permissions on the shared folder.

The user cannot access the file share.

However when i do the exact same actions on the 2nd domain controller on the domain it works perfectly fine.
This will of course happen for all users / machines on the network for all file shares on the first server and not for any on the 2nd server.
I have compared the directory's above the fileshare and between the 2 computer i am not able to spot any difference in any permissions.
I have also compared the group policy settings between the 2 domains controllers and all appear to exactly the same. they also exist in the same OU.

Can anyone shed some light on this why the file share can be accessed when they are added to the folder permissions. But cannot when they are a member of a group which is added to the file permissions in exactly the same way.

PS. This is a hard one. Its had me stumped for months.