Calling unmanage code from WPF 4.5 cause problems

Hi all of you,

I'm using this code in order to remove close button in one Window object.

Imports System.Runtime.InteropServices
Imports System.Windows.Interop
Partial Public Class Rendimientos
    Inherits Window
    Private Const MF_BYPOSITION As Integer = 1024
    Private Const MF_DISABLED As Integer = 2
    Private Const MF_REMOVE As Integer = 4096<DllImport("user32.dll")> _
    Private Shared Function GetSystemMenu(hwnd As IntPtr, revert As Integer) As IntPtr
    End Function<DllImport("user32.dll")> _
    Private Shared Function GetMenuItemCount(hmenu As IntPtr) As Integer
    End Function<DllImport("user32.dll")> _
    Private Shared Function RemoveMenu(hmenu As IntPtr, npos As Integer, wflags As Integer) As Integer
    End Function<DllImport("user32.dll")> _
    Private Shared Function DrawMenuBar(hwnd As IntPtr) As Integer
    End Function


    Public Sub Rendimientos()
        Try
            InitializeComponent()

            AddHandler Me.SourceInitialized, AddressOf Rendimientos_SourceInitialized

        Catch ex As Exception

            MessageBox.Show(ex.Message)
        End Try

    End Sub
    Public Sub Rendimientos_SourceInitialized(sender As Object, e As EventArgs)

        Dim helper As New WindowInteropHelper(Me)
        Dim windowHandle As IntPtr = helper.Handle
        Dim hmenu As IntPtr = GetSystemMenu(windowHandle, 0)
        Dim cnt As Integer = GetMenuItemCount(hmenu)

        RemoveMenu(hmenu, cnt - 1, MF_DISABLED Or MF_BYPOSITION)

        RemoveMenu(hmenu, cnt - 2, MF_DISABLED Or MF_BYPOSITION)

        DrawMenuBar(windowHandle)

    End Sub

End Class

No results for this code when I run my Window object from my page.

Close button keeps visible...

Problem (I think) happen because I do not put "EntryPoint" in every definition.

But, unfortunately If I put EntryPoint Visual Studio compiler denounces:

"EntryPoint is not declared. It may be inaccessible due to its protection level"

I'm stuck with that, help me out!

Primary platform is Windows 7 Ultimate 64 bit along with VS 2012/Sql2k8 for WPF and SilverLight stuff