Como manipular FNERR_BUFFERTOOSMALL no Windows

extern "C"
{
WNDPROC* g_lpfnDialogProc =NULL;


unsigned int CALLBACK DialogHook(HWND hwnd, UINT uMsg, WPARAM wParam,
                          LPARAM lParam)
{
	static HWND hwndParentDialog;
	LPOFNOTIFY lpofn;
	int cbLength;
	static LPTSTR lpsz;
	static int LastLen;
	
	switch (uMsg)
	{
	case WM_INITDIALOG:
          // You need to use a copy of the OPENFILENAME struct used to
          // create this dialog. You can store a pointer to the
          // OPENFILENAME struct in the ofn.lCustData so you can
          // retrieve it here in the lParam. Once you have it, you
          // need to hang on to it. Using window properties provides a
          // good thread safe solution to using a global variable.

          if(!SetProp(GetParent(hwnd), "OFN", (void *) lParam))
	  MessageBox(NULL, "SET PRop Failed", "ERROR", MB_OK);
          return (0);

	  case WM_COMMAND:
		  {
			OutputDebugString("command\n");
		  }
		  break;
      case WM_NOTIFY:
          // The OFNOTIFY struct is passed in the lParam of this
          // message.

          lpofn = (LPOFNOTIFY) lParam;

          switch (lpofn->hdr.code)
          {
 	  	case CDN_SELCHANGE:
			  
		LPOPENFILENAME lpofn;
		cbLength = CommDlg_OpenSave_GetSpec(GetParent(hwnd), NULL, 0);
		  
		cbLength += _MAX_PATH;
		
   	     // The OFN struct is stored in a property of dialog window
			  		  
		lpofn = (LPOPENFILENAME) GetProp(GetParent(hwnd),
						  "OFN");
			
		if (lpofn->nMaxFile < cbLength)  

		{
			  // Free the previously allocated buffer.
			  if(lpsz)
				  HeapFree(GetProcessHeap(),
							0,
 				 	                lpsz);
  			 // Allocate a new buffer
			  lpsz = (LPTSTR) HeapAlloc(GetProcessHeap(),
						HEAP_ZERO_MEMORY,
						cbLength);
			  if (lpsz)
			  {
					  
				  lpofn->lpstrFile = lpsz;
				  lpofn->nMaxFile  = cbLength;
			  }
		  }
		  break;
			  
         }
          return (0);

      case WM_DESTROY:

          // Also need to free the property with the OPENFILENAME
          // struct.
          RemoveProp(GetParent(hwnd), "OFN");
          return (0);
  }
  return (0);
}