...
...

  private
    function GetaPipeHandles(iIndex, jIndex: Integer): USB_PIPE_HANDLE;
    procedure SetaPipeHandles(iIndex, jIndex: Integer; const Value: USB_PIPE_HANDLE);
  public
    property aPipeHandles[iIndex: Integer; jIndex :Integer] : USB_PIPE_HANDLE read GetaPipeHandles write SetaPipeHandles;

...
...

function TNotifyUSB.GetaPipeHandles(iIndex, jIndex: Integer): USB_PIPE_HANDLE;
begin
  Result := aPipeHandles[iIndex][jIndex]; // Fehler hier
end;


procedure TNotifyUSB.SetaPipeHandles(iIndex, jIndex: Integer;
  const Value: USB_PIPE_HANDLE);
begin
  aPipeHandles[iIndex][jIndex] := Value; // und Fehler hier
end;