Question

Sub CboSO_DropDown(ByVal sender As Object, ByVal e As System.EventArgs) Handles CboSO.DropDown
        If functionmode = "UPDATE" Then
            Dim daProp2 As New OdbcDataAdapter()
            Dim dsProp2 As New DataSet()
            Dim qryProp2 As String


            qryProp2 = "SELECT num FROM so WHERE scn = '" & txtSCN.Text & " '"
            daProp2.SelectCommand = New OdbcCommand(qryProp2, conn)
            Dim cb2 As OdbcCommandBuilder = New OdbcCommandBuilder(daProp2)
            daProp2.Fill(dsProp2, "so")
            Dim dtRbt As DataTable = dsProp2.Tables("so")

            Try
                If dsProp2.Tables(0).Rows.Count > 0 Then
                    CboSO.DropDownStyle = ComboBoxStyle.DropDownList
                    CboSO.DataSource = dsProp2
                    CboSO.DisplayMember = "num"

                End If

            Catch ex As OdbcException
                MsgBox(ex.ToString)
            Finally
                conn.Close()
            End Try
        End If
    End Sub

Answer 1

Assign the DataTable object reference.

 CboSO.DataSource = dtRbt
 CboSO.DisplayMember = "num"