Can't get BuildExplicitAccessWithName API to work in 64-bit VB.Net

Imports System.Runtime.InteropServices
 
Module Module1
 
    Private Const CONTAINER_INHERIT_ACE As Integer = &H2
    Private Const OBJECT_INHERIT_ACE As Integer = &H1
    Private Const SET_ACCESS As Integer = &H2
 
    Private Const SYNCHRONIZE As Integer = &H100000
    Private Const READ_CONTROL As Integer = &H20000
    Private Const WRITE_DAC As Integer = &H40000
    Private Const WRITE_OWNER As Integer = &H80000
    Private Const STANDARD_RIGHTS_READ As Integer = (READ_CONTROL)
    Private Const STANDARD_RIGHTS_WRITE As Integer = (READ_CONTROL)
    Private Const DELETE As Integer = &H10000
    Private Const FILE_DELETE_CHILD As Integer = &H40
    Private Const FILE_ALL_ACCESS As Integer = &HF0000 Or SYNCHRONIZE Or &H1FF
 
    'typedef struct _TRUSTEE {
    '  PTRUSTEE pMultipleTrustee;
    '  MULTIPLE_TRUSTEE_OPERATION MultipleTrusteeOperation;
    '  TRUSTEE_FORM TrusteeForm;
    '  TRUSTEE_TYPE TrusteeType;
    '  LPTSTR ptstrName;
    '} TRUSTEE, *PTRUSTEE;
    <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
    Public Structure TRUSTEE
        Dim pMultipleTrustee As IntPtr
        Dim MultipleTrusteeOperation As Integer
        Dim TrusteeForm As Integer
        Dim TrusteeType As Integer
        'Dim ptstrName As String
        Dim ptstrName As IntPtr
    End Structure
 
    'typedef struct _EXPLICIT_ACCESS {
    '  DWORD grfAccessPermissions;
    '  ACCESS_MODE grfAccessMode;
    '  DWORD grfInheritance;
    '  TRUSTEE Trustee;
    '} EXPLICIT_ACCESS, *PEXPLICIT_ACCESS;
    <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
    Public Structure EXPLICIT_ACCESS
        Dim grfAccessPermissions As Integer
        Dim grfAccessMode As Integer
        Dim grfInheritance As Integer
        Dim Trustee As TRUSTEE
    End Structure
 
    'VOID BuildExplicitAccessWithName(
    '  PEXPLICIT_ACCESS pExplicitAccess,
    '  LPTSTR pTrusteeName,
    '  DWORD AccessPermissions,
    '  ACCESS_MODE AccessMode,
    '  DWORD Inheritance
    ');
    Declare Auto Sub BuildExplicitAccessWithName Lib "AdvAPI32.DLL" ( _
        ByVal pExplicitAccess As IntPtr, _
        ByVal pTrusteeName As String, _
        ByVal AccessPermissions As Integer, _
        ByVal AccessMode As Integer, _
        ByVal Inheritance As Integer _
    )
 
    Sub Main()
        Dim ea As New EXPLICIT_ACCESS
        Dim p As IntPtr
 
        ' allocate a chunk of memory that *way* over the requirement
        p = Marshal.AllocHGlobal(256)
        Console.WriteLine("starting")
        BuildExplicitAccessWithName(p, "Users", FILE_ALL_ACCESS, SET_ACCESS, CONTAINER_INHERIT_ACE Or OBJECT_INHERIT_ACE)
        Console.WriteLine("finished")
 
        ' cast it back to the structure to see if things line up
        ea = CType(Marshal.PtrToStructure(p, GetType(EXPLICIT_ACCESS)), EXPLICIT_ACCESS)
        Console.WriteLine("ea.grfAccessPermissions=" & ea.grfAccessPermissions)
        Console.WriteLine("ea.grfAccessMode=" & ea.grfAccessMode)
        Console.WriteLine("ea.grfInheritance=" & ea.grfInheritance)
        Console.WriteLine("ea.Trustee.pMultipleTrustee=" & ea.Trustee.pMultipleTrustee)
        Console.WriteLine("ea.Trustee.MultipleTrusteeOperation=" & ea.Trustee.MultipleTrusteeOperation)
        Console.WriteLine("ea.Trustee.TrusteeForm=" & ea.Trustee.TrusteeForm)
        Console.WriteLine("ea.Trustee.TrusteeType=" & ea.Trustee.TrusteeType)
        'Console.WriteLine("ea.Trustee.ptstrName='" & ea.Trustee.ptstrName & "'")
        Console.WriteLine("ea.Trustee.ptstrName=" & ea.Trustee.ptstrName)
 
        ' ignore the structure and look at the raw data
        For i As Integer = 0 To 47
            Debug.WriteLine("i=" & i & ", byte=" & Hex(Marshal.ReadByte(p, i)))
            If i Mod 4 = 3 Then
                Debug.WriteLine("")
            End If
        Next
 
        ' OK... the pointer that holds the string has been truncated... it only has 32-bits populated
        Dim buf() As Byte = BitConverter.GetBytes(ea.Trustee.ptstrName)
        For Each b As Byte In buf
            Console.Write("{0:X2} ", b)
        Next
 
        Console.ReadLine()
    End Sub
 
End Module

                                              

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