[ c# ] NullRefferenceException

Torej, sledeco kodo sem skopiral z neta (no, ne cisto vse, tisto if in naprej dol).

public bool startMonitoring()
{
   IntPtr pNotifyInfo = IntPtr.Zero;
   IntPtr handle = IntPtr.Zero;
   int change = 0;
   int waitResult = 0;

   handle = FindFirstPrinterChangeNotification(hPrinter, PRINTER_CHANGE_JOB, 0, IntPtr.Zero);
   waitResult = WaitForSingleObject(handle, INFINITE);

   if ( FindNextPrinterChangeNotification(handle, ref change, IntPtr.Zero, out pNotifyInfo)) 
   {
      PRINTER_NOTIFY_INFO info = (PRINTER_NOTIFY_INFO) Marshal.PtrToStructure (pNotifyInfo, typeof (PRINTER_NOTIFY_INFO));     
      int pData = (int)pNotifyInfo + Marshal.SizeOf( ypeof(PRINTER_NOTIFY_INFO));
      PRINTER_NOTIFY_INFO_DATA[] data = new PRINTER_NOTIFY_INFO_DATA[info.Count];
      for ( uint i = 0; i < info.Count; i++ )
      {
         data[i] = (PRINTER_NOTIFY_INFO_DATA)Marshal.PtrToStructure((IntPtr)pData, typeof(PRINTER_NOTIFY_INFO_DATA));
         pData += Marshal.SizeOf( typeof(PRINTER_NOTIFY_INFO_DATA));
      }
      FreePrinterNotifyInfo( pNotifyInfo );
      Console.WriteLine("konec branja strukture");
   }
   return false;
}

pred tem pa imam deklarirani strukturi v istem razredu

struct PRINTER_NOTIFY_INFO
 { 
	public uint Version; 
	public uint Flags; 
	public uint Count; 
	// Array of PRINTER_NOTIFY_INFO_DATA follows
}

struct PRINTER_NOTIFY_INFO_DATA
{
        public ushort Type; 
	public ushort Field; 
	public uint Reserved; 
	public uint Id; 
	public uint cbBuf;  // or adwData[0]
	public IntPtr pBuf; // or uint adwData[1]
}

Ob prevajanju te kode mi javi warning

PRINTER_NOTIFY_INFO.Version' is never assigned to, and will always have its default value 0

ob izvajanju prve vrstice znotraj if-a pa tisti slavni

System.NullReferenceException: Object reference not set to an instance of an object.

Tu imam pa toliko stvari, da ne vem, kateri ogjekt zadeva misli. Se komu kaj vec sanja?

Ja, ekekec, to je bilo to. Nic se ni tja noter zapisalo. In ko sem se se malo poglobil v MSDN, sem opazil, da s tistim IntPtr.Zero sploh ne zahtevam podatkov. Tako sem deklariral se eno strukturo PRITNER_NOTIFY_OPTIONS

struct PRINTER_NOTIFY_OPTIONS
{
	public uint Version; 
	public uint Flags; 
	public uint Count;
	public IntPtr buf;
}

in jo porinil na tisto mesto v klicu procedure, kjer je bila potrebna. tistega buf se sploh nisem dotika, ker sem flags nastavil na PRINTER_NOTIFY_OPTIONS_REFRESH, in bi torej ta funkcija morala vse druge clane te strukture ignorirati.
Sedaj pa dobim NullRefferenceException v klicu funkcije FindNexPrinterChangeNotification(). In mi se zmeraj ni jasno, kaj je narobe. Kaj bi pa sedaj, laho bilo 0?