When I assign a link to Domain Users, the users never get the link. If I assign the link directly to the user or another group, then things work.

 

This is a feature/limitation of Microsoft Active Directory (MS AD). Domain Users is typically the Primary Group that every domain user gets added to. Because of the 5000 user limitation in Microsoft Groups, they don’t store the user's ID in the Domain Users group, and the user's ID in MS AD does not contain Domain Users in its list of group memberships. Instead, the user's ID contains the RID of the Domain Users group stored in the PrimaryGroupID attribute.  Due to this behavior UW is unable to utilize a Primary Group for assignments.

See the following URL for more information http://support.microsoft.com/default.aspx?scid=kb;en-us;275523

This 5000 user limitation came from Windows 2000.  Windows 2003, and higher, removes the limitation, but the Primary Group is still used in the same way.