error comes at the time of add ,update and delete function

Imports System.Data.SqlClient

Public Class view1
    Inherits System.Web.UI.Page


    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Button1.DataBinding
        If Not IsPostBack Then
            BindGridView()
        End If
    End Sub

    Private Function GetConnectionString() As String
        Return System.Configuration.ConfigurationManager.ConnectionStrings("nitink").ConnectionString
    End Function

    Private Sub BindGridView()
        Dim Customer As New DataTable()
        Dim connection As New SqlConnection("Data Source=KARANDE\sqlexpress;Initial Catalog=nitink;Integrated Security=True")
        Try
            connection.Open()
            Dim sqlStatement As String = "SELECT Top(10)* FROM Customer"
            Dim cmd As New SqlCommand(sqlStatement, connection)
            Dim sqlDa As New SqlDataAdapter(cmd)

            sqlDa.Fill(Customer)
            If Customer.Rows.Count > 0 Then
                GridView1.DataSource = Customer
                GridView1.DataBind()
            End If
        Catch ex As System.Data.SqlClient.SqlException
            Dim msg As String = "Fetch Error:"
            msg += ex.Message
            Throw New Exception(msg)
        Finally
            connection.Close()
        End Try
    End Sub

    Private Sub UpdateOrAddNewRecord(ByVal ID As String, ByVal Company As String, ByVal Name As String, ByVal Title As String, ByVal Address As String, ByVal CounTry As String, ByVal isUpdate As Boolean)
        Dim connection As SqlConnection = New SqlConnection("Data Source=KARANDE\sqlexpress;Initial Catalog=nitink;Integrated Security=True")
        Dim sqlStatement As String = String.Empty

        If Not isUpdate Then
            sqlStatement = "INSERT INTO Customer" + "(CustomerID,CompanyName,ContactName,ContactTitle,Address,Country)" +
"VALUES (@CustomerID,@CompanyName,@ContactName,@ContactTitle,@Address,@Country)"
        Else
            sqlStatement = "UPDATE Customer" + "SET CompanyName = @CompanyName,ContactName = @ContactName," + "ContactTitle = @ContactTitle,Address = @Address,Country = @Country" + "WHERE CustomerID = @CustomerID,"
        End If
        Try
            connection.Open()
            Dim cmd As SqlCommand = New SqlCommand(sqlStatement, connection)
            cmd.Parameters.AddWithValue("@CustomerID", ID)
            cmd.Parameters.AddWithValue("@CompanyName", Company)
            cmd.Parameters.AddWithValue("@ContactName", Name)
            cmd.Parameters.AddWithValue("@ContactTitle", Title)
            cmd.Parameters.AddWithValue("@Address", Address)
            cmd.Parameters.AddWithValue("@Country", CounTry)
            cmd.CommandType = CommandType.Text
            cmd.ExecuteNonQuery()
        Catch ex As System.Data.SqlClient.SqlException
            Dim msg As String = "Insert/Update Error:"
            msg += ex.Message
            Throw New Exception(msg)

        Finally
            connection.Close()
        End Try
    End Sub

    Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        UpdateOrAddNewRecord(TextBox1.Text, TextBox2.Text, TextBox3.Text, TextBox4.Text, TextBox5.Text, TextBox6.Text, False)

        BindGridView()

    End Sub

    Protected Sub GridView1_RowEditing(sender As Object, e As System.Web.UI.WebControls.GridViewEditEventArgs) Handles GridView1.RowEditing
        GridView1.EditIndex = e.NewEditIndex ' turn to edit mode
        BindGridView()

    End Sub

    Protected Sub GridView1_RowCancelingEdit(sender As Object, e As System.Web.UI.WebControls.GridViewCancelEditEventArgs) Handles GridView1.RowCancelingEdit
        GridView1.EditIndex = -1 'swicth back to default mode
        BindGridView()

    End Sub

    Protected Sub GridView1_RowUpdating(sender As Object, e As System.Web.UI.WebControls.GridViewUpdateEventArgs) Handles GridView1.RowUpdating
        Dim id As String = GridView1.Rows(e.RowIndex).Cells(0).Text  'ID
        Dim company As String = (CType(GridView1.Rows(e.RowIndex).Cells(1).Controls(0), TextBox)).Text  'Company
        Dim name As String = (CType(GridView1.Rows(e.RowIndex).Cells(2).Controls(0), TextBox)).Text  'Name
        Dim title As String = (CType(GridView1.Rows(e.RowIndex).Cells(3).Controls(0), TextBox)).Text  'Title
        Dim address As String = (CType(GridView1.Rows(e.RowIndex).Cells(4).Controls(0), TextBox)).Text  'Address
        Dim counTry As String = (CType(GridView1.Rows(e.RowIndex).Cells(5).Controls(0), TextBox)).Text  'Country

        Dim UpdateOrAddNewRecord(id, company, name, title, address, counTry, True)
        GridView1.EditIndex = -1
        BindGridView()
    End Sub



    Private Sub DeleteRecord(ByVal ID As String)
        Dim connection As SqlConnection = New SqlConnection("Data Source=KARANDE\sqlexpress;Initial Catalog=nitink;Integrated Security=True")
        Dim sqlStatement As String = "DELETE FROM Customer WHERE CustomerID = @CustomerID"
        Try
            connection.Open()
            Dim cmd As SqlCommand = New SqlCommand(sqlStatement, connection)
            cmd.Parameters.AddWithValue("@ID", ID)
            cmd.CommandType = CommandType.Text
            cmd.ExecuteNonQuery()
        Catch ex As System.Data.SqlClient.SqlException
            Dim msg As String = "Deletion Error:"
            msg += ex.Message
            Throw New Exception(msg)

        Finally 'this is the error spot 
            connection.Close()
        End Try
    End Sub




    Protected Sub GridView1_RowDeleting(sender As Object, e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles GridView1.RowDeleting
        Dim id As String = GridView1.Rows(e.RowIndex).Cells(0).Text
        DeleteRecord(id) 'call delete method
        BindGridView() 'rebind grid to reflect changes made

    End Sub
End Class