Symbian Direct Screen Access Example problem

Dear all,
It is my first time to create a direct screen access program on Symbian 
Series 60.
I used the example downloaded from nokia, however, I met a link problem.
error LNK2001: unresolved external symbol "public: static class 
CWbxVideoPlayerTest * __cdecl CWbxVideoPlayerTest::NewL(

Here is my code:
// Test.h
//------------------------------------------------------------------------
#ifndef DIRECTDISPLAYENG_H
#define DIRECTDISPLAYENG_H

#include <w32std.h>

//class CDirectDisplayRender;

enum DirectDisplayPanics{
 DirectDisplayStarted = 1,
 DirectDisplayStopped
};

const TInt KGenerationInterval = 10000;

_LIT(KDirectDisplayTxt, "Video");

class PlayerTest : public CTimer, public MDirectScreenAccess{
 // Construction & destruction
 public:

  static PlayerTest * NewL(
   // The current window server session owned by the application
   RWsSession& aClient,
   // The default screen device for the application
   CWsScreenDevice& aScreenDevice,
   // The RWindow associated with a control.
   RWindow& aWindow,
   TInt aUserFrameBuffer
  );

 ~PlayerTest ();

 private:
  // private constructors - use NewL to call it
  PlayerTest (
   /*
   * Window server handling
   */
   // The current window server session owned by the application
   RWsSession& aClient,
   // The default screen device for the application
   CWsScreenDevice& aScreenDevice,
   // The RWindow associated with a control.
   RWindow& aWindow,
   TInt aUserFrameBuffer
   );

  void ConstructL();

 public:
  void StartDrawingL();
  void StopDrawing();
  // Are we drawing?
  inline TBool Drawing() {return iDrawing;}

 private:
  void RunL();
  void DoCancel();

 private:
  // Implement MDirectScreenAccess
  void Restart(RDirectScreenAccess::TTerminationReasons aReason);
  void AbortNow(RDirectScreenAccess::TTerminationReasons aReason);

 private:
  // Window Server handling
  RWsSession& iClient;
  CWsScreenDevice& iScreenDevice;
  RWindow& iWindow;

  // Direct Screen Access
  CDirectScreenAccess* iDirectScreenAccess;
  CFbsBitGc* iGc;
  RRegion* iRegion;

  // Are we drawing?
  TBool iDrawing;

  TInt iUserFrameBuffer;

  TRect iFlagRect;
  TInt iFrameBufLen;

  TPoint iPosition;
};
#endif
//------------------------------------------------------------------------

// Container.cpp
void PlayerContainer::ConstructL(const TRect& aRect)
    {
    CreateWindowL();

    iLabel = new (ELeave) CEikLabel;
    iLabel->SetContainerWindowL( *this );
    iLabel->SetTextL( _L("Example View") );

 SetRect(aRect);

 iTest = PlayerTest ::NewL(iEikonEnv->WsSession(),
                               *(CCoeEnv::Static()->ScreenDevice()),
                Window(), 0);

    ActivateL();
    }


If i do not run the iTest = PlayerTest::NewL(..
Then, there is not any error,
I wanna ask anyone can help me to solve this program?
Thanks a lot