ช่วยดูหน่อยครับ Error เวลากด add เพื่อบันทึกข้อมูล asp.net (VB)

Imports System.Data
Imports System.Data.SqlClient

Public Class Home
    Inherits System.Web.UI.Page

    Dim objConn As SqlConnection
    Dim strConnString, strSQL As String
    Dim objCmd As SqlCommand

    Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        strConnString = "Server=localhost;UID=sa;PASSWORD=1234;database=mydata;Max Pool Size=400;Connect Timeout=600;"
        objConn = New SqlConnection
        objConn.ConnectionString = strConnString
        objConn.Open()

        If Not Page.IsPostBack() Then
            BindData()
        End If
    End Sub
    Sub BindData()

        Dim strSQL As String

        strSQL = "SELECT * FROM Detail"

        Dim dtReader As SqlDataReader
        objCmd = New SqlCommand(strSQL, objConn)
        dtReader = objCmd.ExecuteReader()

        '*** BindData to GridView ***'
        myGridView.DataSource = dtReader
        myGridView.DataBind()

        dtReader.Close()
        dtReader = Nothing

    End Sub
        Sub Page_UnLoad()
            objConn.Close()
            objConn = Nothing
        End Sub
        Sub modEditCommand(ByVal sender As Object, ByVal e As GridViewEditEventArgs)
            myGridView.EditIndex = e.NewEditIndex
            myGridView.ShowFooter = False
            BindData()
        End Sub

        Sub modCancelCommand(ByVal sender As Object, ByVal e As GridViewCancelEditEventArgs)
            myGridView.EditIndex = -1
            myGridView.ShowFooter = True
            BindData()
        End Sub

        Sub modDeleteCommand(ByVal sender As Object, ByVal e As GridViewDeleteEventArgs)

            strSQL = "DELETE FROM Detail WHERE ComputerName = '" & myGridView.DataKeys.Item(e.RowIndex).Value & "'"
            objCmd = New SqlCommand(strSQL, objConn)
            objCmd.ExecuteNonQuery()

            myGridView.EditIndex = -1
            BindData()
        End Sub
        Protected Sub myGridView_RowCommand(ByVal sender As Object, ByVal e As GridViewCommandEventArgs) Handles myGridView.RowCommand

            If e.CommandName = "Add" Then
                '*** Computer name ***'
                Dim txtComputerName As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerName"), TextBox)
                '*** User Name ***'
                Dim txtUserName As TextBox = CType(myGridView.FooterRow.FindControl("txtAddUserName"), TextBox)
                '*** IP Address ***'
                Dim txtIPAddress As TextBox = CType(myGridView.FooterRow.FindControl("txtAddIPAddress"), TextBox)
                '*** Domain name ***'
                Dim txtDomainName As TextBox = CType(myGridView.FooterRow.FindControl("txtAddDomainName"), TextBox)
                '*** Section ***'
                Dim txtSection As TextBox = CType(myGridView.FooterRow.FindControl("txtAddSection"), TextBox)
                '*** Telephone Number ***'
                Dim txtTelephone As TextBox = CType(myGridView.FooterRow.FindControl("txtAddTelephone"), TextBox)
                '*** Com Purchase date ***'
                Dim txtComputerPurchaseDate As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerPurchaseDate"), TextBox)
                '*** Com purchase expire ***'
                Dim txtComputerPurchaseExpire As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerPurchaseExpire"), TextBox)
                '*** ComputerBand ***'
                Dim txtComputerBand As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerBand"), TextBox)
                '*** ComputerModel ***'
                Dim txtComputerModel As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerModel"), TextBox)
                '*** Com Serial ***'
                Dim txtComputerSerialNo As TextBox = CType(myGridView.FooterRow.FindControl("txtAddComputerSerialNo"), TextBox)
                '*** Spec Computer ***'
                Dim txtSpecComputer As TextBox = CType(myGridView.FooterRow.FindControl("txtAddSpecComputer"), TextBox)
                '*** OS ***'
                Dim txtOS As TextBox = CType(myGridView.FooterRow.FindControl("txtAddOS"), TextBox)
                '*** License Key ***'
                Dim txtLicenseKey As TextBox = CType(myGridView.FooterRow.FindControl("txtAddLicenseKey"), TextBox)
                '*** SpecialApp ***'
                Dim txtSpecialApp As TextBox = CType(myGridView.FooterRow.FindControl("txtAddSpecialApp"), TextBox)
                '*** MonitorBand ***'
                Dim txtMonitorBand As TextBox = CType(myGridView.FooterRow.FindControl("txtAddMonitorBand"), TextBox)
                '*** MonitorModel ***'
                Dim txtMonitorModel As TextBox = CType(myGridView.FooterRow.FindControl("txtAddMonitorModel"), TextBox)
                '*** MonitorSerialNo ***'
            Dim txtMonitorSerialNo As TextBox = CType(myGridView.FooterRow.FindControl("txtAddMonitorSerialNo"), TextBox)
                '*** SpecMonitor ***'
                Dim txtSpecMonitor As TextBox = CType(myGridView.FooterRow.FindControl("txtAddSpecMonitor"), TextBox)
                '*** Monitor Purchase date ***'
                Dim txtMonitorPurchaseDate As TextBox = CType(myGridView.FooterRow.FindControl("txtAddMonitorPurchaseDate"), TextBox)
                '*** Monitor purchase expire ***'
                Dim txtMonitorPurchaseExpire As TextBox = CType(myGridView.FooterRow.FindControl("txtAddMonitorPurchaseExpire"), TextBox)
                '*** Note Remark ***'
                Dim txtNoteRemark As TextBox = CType(myGridView.FooterRow.FindControl("txtAddNoteRemark"), TextBox)

            strSQL = "INSERT INTO Detail (ComputerName,UserName,IPAddress,DomainName,Section,Telephone, ComputerPurchaseDate,ComputerPurchaseExpire,ComputerBand, ComputerModel,ComputerSerialNo,SpecComputer,OS,LicenseKey, SpecialApp,MonitorBand,MonitorModel,MonitorSerialNo,SpecMonitor, MonitorPurchaseDate,MonitorPurchaseExpire,NoteRemark) " & _
            " VALUES ('" & txtComputerName.Text & "','" & txtUserName.Text & "' ,'" & txtIPAddress.Text & "','" & txtDomainName.Text & "','" & txtSection.Text & "','" & txtTelephone.Text & "', '" & txtComputerPurchaseDate.Text & "','" & txtComputerPurchaseExpire.Text & "','" & txtComputerBand.Text & "' ,'" & txtComputerModel.Text & "','" & txtComputerSerialNo.Text & "','" & txtSpecComputer.Text & "', '" & txtOS.Text & "','" & txtLicenseKey.Text & "','" & txtSpecialApp.Text & "','" & txtMonitorBand.Text & "' ,'" & txtMonitorModel.Text & "','" & txtMonitorSerialNo.Text & "','" & txtSpecMonitor.Text & "','" & txtMonitorPurchaseDate.Text & "' ,'" & txtMonitorPurchaseExpire.Text & "','" & txtNoteRemark.Text & "',) "

            objCmd = New SqlCommand(strSQL, objConn)
            objConn.Close()
            objConn = Nothing


            BindData()

            End If
        End Sub