nested datalist

håller på att skapa en relation mellan 2 tabeller men får felet..

'column' argument cannot be null.
Parameter name: column

     Dim da1 As OleDbDataAdapter
        Dim ds1 As New DataSet()

        Dim strsqlT As String = "SELECT hund.hundnr, Sum(Utst_resultat.poang) AS p, Count(utstnr) AS antutst, Hund.hundnamn, Hund.kon"
        strsqlT = strsqlT + " FROM Utst_resultat INNER JOIN Hund ON Utst_resultat.hundNr = Hund.hundnr"
        strsqlT = strsqlT + " GROUP BY  Hund.hundnr, Utst_resultat.hundNr, Hund.hundnamn, Hund.kon HAVING ((Not (Sum(Utst_resultat.poang))=0) AND ((Hund.kon)='H')) ORDER BY Sum(Utst_resultat.poang) DESC;"

         da1 = New OleDbDataAdapter(strsqlT, conString)
        da1.Fill(ds1, "hund")

        Dim strtop As String = "SELECT hundnr AS hnr, Sum(u.poang) AS top5 FROM utst_resultat AS u"
        strtop = strtop + " WHERE (((u.poang) In (select top 5 poang from(utst_resultat)"
        strtop = strtop + " where(hundnr = u.hundnr) order by poang desc))) GROUP BY hundnr "

        da = New OleDbDataAdapter(strsql, conString)
        da.Fill(ds1, "top")

        ds1.Relations.Add(New DataRelation("NestThem", ds1.Tables(0).Columns("hundnr"), ds1.Tables(1).Columns("hnr")))
        dlReshanar.DataSource = ds1
        dlReshanar.DataBind()

här kommer felmedelandet

ds1.Relations.Add(New DataRelation("NestThem", ds1.Tables(0).Columns("hundnr"), ds1.Tables(1).Columns("hnr")))

Det låter som att hundnr eller hnr är null någonstans i dina tabeller.