invalid attempt to call read when reader is closed รบกวนช่วยดูให้หน่อยค่ะ

Dim Count As Integer
        For iSum = 0 To DataGridView1.RowCount - 2
            dtReader.Close()
            variableGoodCode = DataGridView1.Rows(iSum).Cells("goodcode").Value
            variableDocuNo = DataGridView1.Rows(iSum).Cells("docuno").Value
            variableSerial = DataGridView1.Rows(iSum).Cells("serialno").Value
            objCMD.CommandText = "select count (DocuCopyNo) AS CountDocuno from WHHD where DocuCopyNo = '" & variableDocuNo & "'"
            dtReader = objCMD.ExecuteReader
            If dtReader.HasRows Then
                While dtReader.Read()
                    Count = dtReader("CountDocuNo")
                    If Count = 0 Then
                        'Variable For Save
                        MaxDocuID = GetMaxDocuID()
                        CustID = GetCustID(variableDocuNo)
                        DocuNo = GetDocuNo()
                        SubTypeID = 50000
                        BrchID = GetBrchID(variableDocuNo)
                        DocuType = 1702
                        DODPNo = DocuNo
                        DocuCopyNo = variableDocuNo
                        DocuCopyType = 104
                        DocuFlag = "Y"
                        RefID = GetRefID(variableDocuNo)
                        Postdocutype = 107
                        DocuStatus = "N"
                        AlertFlag = "N"
                        DateInsert = GetDate()
                        dtReader.Close() '******
                        strSQL = "INSERT INTO WHHD(DocuID,CustID,DocuNo,SubTypeID,DocuDate,BrchID,DocuType,DODPNo,DocuCopyDate,DocuCopyNo,DocuCopyType,DocuFlag,RefID,Postdocutype,DocuStatus,AlertFlag) VALUES ('" & MaxDocuID & "','" & CustID & "','" & DocuNo & "','" & SubTypeID & "',getdate(),'" & BrchID & "','" & DocuType & "','" & DODPNo & "',getdate(),'" & DocuCopyNo & "','" & DocuCopyType & "','" & DocuFlag & "','" & RefID & "','" & Postdocutype & "','" & DocuStatus & "','" & AlertFlag & "')"
                        objCMD = New SqlCommand(strSQL, conn)
                        objCMD.ExecuteNonQuery()
                    End If
                End While
            End If
        Next