Protected Sub Page_Error(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Error
        Dim ex As Exception = Server.GetLastError()

        'Effettuare delle operazioni per mostrare l'eccezione
        ...

        'Evitare il redirect in qualche modo,con qualcosa simile a
        preventDefault() 
        'oppure
        Return false    
    End Sub

Protected Sub SqlDataSource1_Inserted(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.SqlDataSourceStatusEventArgs) Handles  SqlDataSource1.Inserted
 sql_exception_handler(e)
End Sub

Protected Sub sql_exception_handler(ByVal e As System.Web.UI.WebControls.SqlDataSourceStatusEventArgs)
        If Not e.Exception Is Nothing Then
            Dim s() As String = {}
            Dim msg As String = "Si sono verificati degli errori durante l'esecuzione della query SQL:\n\n---------------------------------------------\n\n" & _
                                e.Exception.Message & "\n\n---------------------------------------------\n\n"

            field_backup(DettaglioMateriali, s)
            e.ExceptionHandled = True

            Session("exception") = msg
        End If
    End Sub

 Protected Sub field_backup(ByVal form As FormView, ByVal except() As String)
        Dim txt As TextBox
        For Each oControl In form.Controls(0).Controls(1).Controls(0).Controls
            Try
                txt = DirectCast(oControl, TextBox)
                If Not except.Contains(txt.ID) Then
                    Session(txt.ID) = txt.Text
                End If
            Catch ex As Exception
            End Try
        Next
    End Sub