ขอความช่อยเหลือหน่อยคับ คือว่าเช็คข้อมูลที่ไม่ซ้ำพอทำรหัสซ้ำในที่แถว1มันจะฟ้อง แต่แถวอื่นมัน Error คับ

Private Sub Butcas_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Butcas.Click
        Dim result As Boolean

        If TextBox2.Text = "" Or TextBox3.Text = "" Or TextBox4.Text = "" Or TextBox5.Text = "" Or TextBox6.Text = "" Or TextBox7.Text = "" Or TextBox8.Text = "" Or TextBox9.Text = "" Then
            MessageBox.Show("กรุณาใส่ข้อมูลให้ครบ", "ผิดพลาด", MessageBoxButtons.OK, MessageBoxIcon.Information)


        ElseIf MessageBox.Show("คุณต้องการบันทึกใช่หรือไม่ ?", "Save", MessageBoxButtons.YesNo, MessageBoxIcon.Warning) = MsgBoxResult.Yes Then

            Dim Check As Boolean = False
            Dim i As Integer
            For i = 0 To DataGridView1.RowCount = 0


                If TextBox1.Text = DataGridView1.Rows.Item(i).Cells(0).Value.ToString Then
                    Check = True


                    MsgBox("รหัสสินค้า : " & TextBox1.Text & " มีอยู่ในระบบอยู่แล้ว")



                Else


                    Dim S1 As New OleDbDataAdapter("insert into Customer(C_ID,FName,SName,Age,Address,Postcode,Telephone,Email,Regis)values('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "','" & TextBox4.Text & "','" & TextBox5.Text & "','" & TextBox6.Text & "','" & TextBox7.Text & "','" & TextBox8.Text & "','" & TextBox9.Text & "')", conn)
                    Dim S2 As New DataTable
                    S1.Fill(S2)
                    DataGridView1.DataSource = S2
                    ds.Tables("database.mdb").Clear()
                    Showee()

                    TextBox1.Text = ""
                    TextBox2.Text = ""
                    TextBox3.Text = ""
                    TextBox4.Text = ""
                    TextBox5.Text = ""
                    TextBox6.Text = ""
                    TextBox7.Text = ""
                    TextBox8.Text = ""
                    txtSearch.Text = ""

                End If
                Exit For
            Next


        Else
                result = True

        End If

    End Sub