I have this code and I am getting the above error msg (Err.Num 35603)

Code:
Do While Not rs.EOF
     Set lvwItem = lvwMain.ListItems.Add(, rs!Memb_ID.Value, rs!First_Name.Value & " " & _
                IIf(rs!Middle_Name.Value = "", rs!Surname.Value, rs!Middle_Name.Value & " " & _
                                              rs!Surname.Value))
    rs.MoveNext
Loop
rs!Memb_ID.Value is the primary key in the database.
Can't you use this?