Thank you for the reply.

I was doing the data binding process in de Page_Load event. I change this to the InitializeDataSource event and the error screen change. Now is the attachment file.

 Protected Sub WebGrid2_InitializeDataSource(sender As Object, e As ISNet.WebUI.WebGrid.DataSourceEventArgs) Handles WebGrid2.InitializeDataSource
        Dim Consultas As New Consultas
        Dim Acceso As New AccesoDatos
        Dim Funciones As New Funciones
        Dim tabla As New DataTable
        'tabla = Consultas.ConsultaCategorias()
        'Dim Total As Int32 = Funciones.SumarGrid(tabla, "Clientes")
        'Funciones.AddColPromedio(tabla, 1, 2, Total)
        'Funciones.AddColCodigo(tabla)
        'WebGrid1.DataSource = tabla
        'WebGrid1.DataBind()
        Dim tabla2 As New DataTable
        tabla2 = Consultas.ConsultaDuraciones()
        Dim Total As Int32 = Funciones.SumarGrid(tabla2, "Clientes")
        Funciones.AddColPromedio(tabla2, 1, 2, Total)
        WebGrid2.DataSource = tabla2
        WebGrid2.DataBind()
    End Sub

 This is the code behind.