ช่วยดูให้หน่อยครับ ไม่รู้มัน Error ตรงไหน แล้วจะแก้ยังไงคับ

  Dim b As Integer
                    For b = 0 To DataGridView2.Rows.Count - 1
                        sb.Remove(0, sb.Length)
                  Error ตรงนี้อะคับ ---->     sb.Append("select TOP 1 Doc_No from cg_pos_head where OU_Code='" & DataGridView2.Rows(b).Cells(0).Value.ToString() & "'order by Doc_No desc")
                        Dim sqlcg_pos_head As String = sb.ToString()
                        com = New SqlCommand
                        With com
                            .CommandType = CommandType.Text
                            .CommandText = sqlcg_pos_head
                            .Parameters.Clear()
                            .Connection = con
                            dr = .ExecuteReader()
                            If dr.HasRows Then
                                dt = New DataTable
                                dt.Load(dr)
                                batid = dt.Rows(0)("Doc_No").ToString()
                                batid2 = CInt(batid) + 1
                                batNO = batid2.ToString("000000")
                            Else

                                batNO = batid2.ToString("000000")
                            End If
                            dr.Close()
                             End With
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