create groups in AD

I have a network which has been migrated from Windows NT to Windows 2000 AD in native mode

Have been able to create a global security group with 5 users.
Have created a Domain Local security group with the Global group as a member.

When I apply the Domain Local group in the permissions of a folder the users are not granted access.

If I put the individual users in the permissions access is granted.

There is also another group access which works that has been migrated from the old NT network which has identicai settings. e.g.
Users in global group - Global group in Local group and local group has the permissions.

Could someone help with an explanation. Could be quite simple for the right person