[VB.Net] Verificare lo stato di una finestra attraverso l'handle

[MatteoG.]

Salve,

ho un problema che nn riesco a risolvere sto provando a verificare lo stato di una finestra conoscendone l'handle, riporto qui sotto il codice. Il problema è che la
GetWindowPlacement mi restituisce sempre ZERO, ossia un errore

la api getlasterror mi da errore numero 126)

Qualcuno sa indicarmi l'errore se c'è ? O come posso fare per verificare lo stato di una finestra partendo dal suo handle ?

Grazie mille !!

Ciao

Public Class Form1
    Inherits System.Windows.Forms.Form

    Public Structure RECT
        Dim Left As Integer
        Dim Top As Integer
        Dim Right As Integer
        Dim Bottom As Integer
    End Structure

    Public Structure POINTAPI
        Dim x As Integer
        Dim y As Integer
    End Structure

    Public Structure WINDOWPLACEMENT
        Dim Length As Integer
        Dim flags As Integer
        Dim showCmd As Integer
        Dim ptMinPosition As POINTAPI
        Dim ptMaxPosition As POINTAPI
        Dim rcNormalPosition As Rect
    End Structure

    Public Declare Function GetWindowPlacement Lib "user32" Alias "GetWindowPlacement" (ByVal hwnd As Integer, ByVal lpwndpl As WINDOWPLACEMENT) As Integer
    Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim handle As Long
        Dim WinEst As WINDOWPLACEMENT
        Dim rtn As Long

        handle = (FindWindow(Nothing, "Senza nome - Blocco note"))
        MsgBox("find : " & handle)
        WinEst.Length = Len(handle)
        rtn = GetWindowPlacement(handle, WinEst)
        MsgBox("Ritorna : " & rtn)

    End Sub
End Class