codice:
    Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim lb As LinkButton = DirectCast(sender, LinkButton)
        PrintLn(lb.CommandName, "CommandName")
        PrintLn(lb.CommandArgument, "CommandArgument")
        
    End Sub

Dalle vostre parti non si usa il cast?