球高人帮我看看这错在哪了。

Imports System.Data.SqlClient
Imports System.Data
Public Class Form1
    Dim cn As SqlConnection
    Dim da As SqlDataAdapter
    Dim ds As DataSet
    Dim dt As DataTable
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            cn = New SqlConnection()
            cn.ConnectionString = "Data Source=XP-201311231519;Initial Catalog=小型数据库;Integrated Security=False;User ID=sa;Password=123456;"
            cn.Open()
            da = New SqlDataAdapter("select * from 加工量", cn)
            ds = New DataSet
            da.Fill(ds, "mytb1")
            Dim dr As DataRow
            dr = ds.Tables("mytb1").NewRow
            For i = 0 To DataGridView1.Rows.Count - 1
                dr("产品编码") = DataGridView1.Rows(i).Cells(1).Value
                dr("产品名称") = DataGridView1.Rows(i).Cells(2).Value
                dr("批次") = DataGridView1.Rows(i).Cells(3).Value
                ds.Tables("mytb1").Rows.Add(dr)
                Dim scb As New SqlCommandBuilder(da)
                da.Update(ds, "mytb1")
                DataGridView1.DataSource = ds.Tables("mytb1")
            Next
            cn.Close()
        Catch ex As Exception
        End Try
    End Sub
End Class
要不帮我看一下这个，为什么会有问题？就是dr("产品编码") = DataGridView1.Rows(i).Cells(1).Value
这句话，Rows(i)这个i用数字代替就可以用不出错，用变量就不行。求高人指点迷津。（代码是从书上抄的，源代码DataGridView1.Rows(i).Cells(1).Value这里是文本框）。
想要用DataGridView1批量更新数据库。