I came upon that little bug the other where Approvers couldn't see the Approve and Reject buttons on a page (that was waiting for approval). The setup is the following:
- Active Directory (2003) users
- The users are part of a global security group in Active Directory
- The Active Directory group is part of the Approvers group in MOSS
If you navigate to the Pages library (View all site content), you can select the "approve" button (contextual) and it will not work either and simply refresh the page. However, if you go in the page's workflows, you can start one there and that process will go through.
However, there's another workaround : Add the Active Directory users directly in the MOSS Approvers group and that will fix the problem. I do not know why but the behaviour isn't the same. Also, I couldn't reproduce the issue with Members, Owners, and Hierarchy Managers so it seems to be only with Approvers.