ติด Error Object reference not set to an instance of an object. แก้ยังไงดีคะ?

Imports System.Data
Imports System.Data.SqlClient
Imports System.Drawing
Imports System.Configuration
Public Class ManageStore
    Inherits System.Web.UI.Page

    Dim con As String = ConfigurationManager.ConnectionStrings("con").ConnectionString

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

        lblMsg.Text = ""

        If Not IsPostBack Then
            Cal1.Visible = False
            loadStore()
        End If

    End Sub

    Protected Sub loadStore()

        Dim SqlCon As New SqlConnection(con)
        Dim cmd As New SqlCommand()
        cmd.CommandText = "SELECT storID,storName,online,active FROM Store"
        cmd.Connection = SqlCon
        SqlCon.Open()
        Dim da As New SqlDataAdapter(cmd)
        Dim ds As New DataSet()
        da.Fill(ds)
        gridStore.DataSource = ds
        gridStore.DataBind()
        SqlCon.Close()

    End Sub

    '*** INSERT ***'
    Protected Sub btnInsert_Click(sender As Object, e As EventArgs) Handles btnInsert.Click

        Dim IsAdded As Boolean = False
        Dim storName As String = txtstorName.Text.Trim()
        Dim online As String = ddlonline.SelectedItem.Value
        Dim active As String = ddlactive.SelectedItem.Value

        Dim sqlCon As New SqlConnection(con)
        Dim cmd As New SqlCommand()
        cmd.CommandText = "INSERT INTO Store(storName,online,active)" & "VALUES(@storName,@online,@active)"
        cmd.Parameters.AddWithValue("@storName", storName)
        cmd.Parameters.AddWithValue("@online", ddlonline.SelectedItem.Value)
        cmd.Parameters.AddWithValue("@active", ddlactive.SelectedItem.Value)
        cmd.Connection = sqlCon
        sqlCon.Open()
        IsAdded = cmd.ExecuteNonQuery() > 0
        sqlCon.Close()

        If IsAdded Then
            lblMsg.Text = "      Added Successfully.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Green
            loadStore()
        Else
            lblMsg.Text = "      Error While Adding.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Red
        End If
        ResetAll()

    End Sub


    '*** UPDATE ***'
    Protected Sub btnUpdate_Click(sender As Object, e As EventArgs) Handles btnUpdate.Click

        If String.IsNullOrEmpty(txtstorID.Text) Then
            lblMsg.Text = "      Please Select Record To Update.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Red
            Return
        End If

        Dim IsUpdated As Boolean = False
        Dim storID As Integer = Convert.ToInt32(txtstorID.Text)
        Dim storName As String = txtstorName.Text.Trim()
        Dim online As String = ddlonline.SelectedItem.Value
        Dim active As String = ddlactive.SelectedItem.Value

        Dim SqlCon As New SqlConnection(con)
        Dim cmd As New SqlCommand()
        cmd.CommandText = "UPDATE Store SET storName=@storName,online=@online,active=@active WHERE storID=@storID"
        cmd.Parameters.AddWithValue("@storID", storID)
        cmd.Parameters.AddWithValue("@storName", storName)
        cmd.Parameters.AddWithValue("@online", ddlonline.SelectedItem.Value)
        cmd.Parameters.AddWithValue("@active", ddlactive.SelectedItem.Value)
        cmd.Connection = SqlCon

        SqlCon.Open()
        IsUpdated = cmd.ExecuteNonQuery() > 0
        SqlCon.Close()

        If IsUpdated Then
            lblMsg.Text = "      Updated Successfully.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Blue
        Else
            lblMsg.Text = "      Error While Updating.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Red
        End If

        gridStore.EditIndex = -1
        loadStore()
        ResetAll()

    End Sub

    '*** DELETE ***'
    Protected Sub btnDelete_Click(sender As Object, e As EventArgs) Handles btnDelete.Click

        If String.IsNullOrEmpty(txtstorID.Text) Then
            lblMsg.Text = "      Please Select Record To Delete.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Red
            Return
        End If

        Dim IsDeleted As Boolean = False
        Dim storID As Integer = Convert.ToInt32(txtstorID.Text)
        Dim storName As String = txtstorName.Text.Trim()
        Dim sqlCon As New SqlConnection(con)
        Dim cmd As New SqlCommand()
        cmd.CommandText = "DELETE FROM Store WHERE storID=@storID"
        cmd.Parameters.AddWithValue("@storID", storID)
        cmd.Connection = sqlCon

        sqlCon.Open()
        IsDeleted = cmd.ExecuteNonQuery() > 0
        sqlCon.Close()

        If IsDeleted Then
            lblMsg.Text = "      Deleted Successfully.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Yellow
        Else
            lblMsg.Text = "      Error While Deleting.....    "
            lblMsg.ForeColor = Color.White
            lblMsg.BackColor = Color.Blue
        End If
        ResetAll()

    End Sub

    '*** CANCEL ***'
    Protected Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click

        ResetAll()

    End Sub

    Protected Sub gridStore_SelectedIndexChanged(sender As Object, e As EventArgs) Handles gridStore.SelectedIndexChanged
        txtstorID.Text = gridStore.DataKeys(gridStore.SelectedRow.RowIndex).Value.ToString()
        txtstorName.Text = (TryCast(gridStore.SelectedRow.FindControl("lblstorName"), Label)).Text
        ddlonline.SelectedItem.Value = (TryCast(gridStore.SelectedRow.FindControl("ddlonline"), DropDownList)).ToString()
        ddlactive.SelectedItem.Value = (TryCast(gridStore.SelectedRow.FindControl("ddlactive"), DropDownList)).ToString()

        btnInsert.Visible = False

    End Sub

    Protected Sub ResetAll()
        btnInsert.Visible = True
        txtstorID.Text = ""
        txtstorName.Text = ""
        ddlonline.SelectedItem.Text = ddlonline.Items.IndexOf(ddlonline.Items.FindByValue("1"))
        ddlactive.SelectedItem.Text = ddlactive.Items.IndexOf(ddlactive.Items.FindByValue("1"))

    End Sub

End Class