I'm trying to add a legitimate LDAP user to a group, both of which exist on the repository, but I'm getting the error "Trustee not found.  [9012]" upon the AddMembersToGroup().  I'm using the code, below.

Anyone have any advice for me?

   AccountReference acctRef = new AccountReference(userName, _session);
        AccountInfo groupAI = Account.GetInfo(groupName, _session);
        AccountReference groupAR = new AccountReference(groupAI);

        System.Collections.Generic.List<string> list = new System.Collections.Generic.List<string>();
        list.Add(userName);
        IEnumerable<string> newlist = list;
        Account.AddMembersToGroup(groupAR, newlist, _session);