Run time error '-2147217908(80040e0c)':

command text was not set for the command object
i have 42 columns i wanted to update whole sheet
i have using this code to update by excel data to mysql 

 Dim i As Integer, QryTxt As String
 
 i = 1
' startrow = 1
 'i = startingrow(Number)
 Do Until startrow = Sheet1.Rows.count
  If Sheet1.Cells(i, 1) = "" Then
   nRows = startrow
   Exit Do
  End If
i = i + 1
 Loop

 For i = 1 To nRows
                QryTxt = QryTxt & "update tblprod_agr_006 set column1 = '" & Replace(Sheet1.Cells(i, 1), "'", "''") & "'," & vbCrLf
                         QryTxt = QryTxt & "    column2 =  '" & Replace(Sheet1.Cells(i, 1), "'", "''") & "'," & vbCrLf
                         QryTxt = QryTxt & "    column3 =  '" & Sheet1.Cells(i, 1) & "'," & vbCrLf
                 QryTxt = QryTxt & "where wds_id =" & "'" & Sheet1.Cells(i, 1) & "'" & "" & vbCrLf

 Next

  cn.Execute (QryTxt)