When creating a GAL from Exchange 2010 SP2 Shell (New-GlobalAddressList) I got the following warning:
WARNING: One or more global address lists were missing from the Active Directory attribute. This is likely caused by using legacy Exchange management tools to create global address lists
Cause: you get this warning if this is the first new GAL created from 2010 or there are 2007 created GALs. This is 'by design' and can be ignored.