Group Membership from script

[thaynej]

For Plone v 2.5 -

I'm trying to add a member to a group from within a script.  I tried this:

          sub_group = pg.getGroupById("Subscribers")
          sub_group.addMember(userName, member)

The addMember method throws an unauthorized exception.  The script does have manager proxy.

What is the correct way to do this?