Account Unknown Error

I have added a group on NT 4.0 SP 4 and then gone to a directory, added the group to the director permissions and then gone back and created another group. I then go to add this group to the same folders permission and notice that the group I just added is showing as Account Unknown.
The group is created on the server as a global group. The folder is on the same server.
I know that this is usually caused by trust being broken between domains but that is not the issue here.
Can anyone shed some light?