Debug Assertion Failed error

Hi

I'm new to programming in Visual C++ so I need some help. I am a BC++ programmer and have used OWL long time, but I want to learn MFC now.

I want to program an application who has only a Property Sheet. I have followed an example of the Kruglinski's book and I have only made one Property Page. The fact is that when I run the program, it sends the message Debug Assertion Failed! Program F:\FMAN\DEBUG\FMAN.EXE  File: afxwin1.inl  Line:22

I have to press the Abort button.
How can I solve it? this is second time that the same error occures but with different applications.

Here is a part of the main application code:
CFman::CFman():Opciones("Manejador de Unidades Fingerscan")
{
      // TODO: add construction code here,
      // Place all significant initialization in InitInstance
}

/////////////////////////////////////////////////////////////////////////////
// The one and only CFman object

CFman theApp;

/////////////////////////////////////////////////////////////////////////////
// CFman initialization

BOOL CFman::InitInstance()
{
      // Standard initialization
      // If you are not using these features and wish to reduce the size
      //  of your final executable, you should remove from the following
      //  the specific initialization routines you do not need.

#ifdef _AFXDLL
      Enable3dControls();                  // Call this when using MFC in a shared DLL
#else
      Enable3dControlsStatic();      // Call this when linking to MFC statically
#endif


      // Since the dialog has been closed, return FALSE so that we exit the
      //  application, rather than start the application's message pump.
      return FALSE;
}

Here's my property sheet class:
CFingerScan::CFingerScan(UINT nIDCaption, CWnd* pParentWnd, UINT iSelectPage)
      :CPropertySheet(nIDCaption, pParentWnd, iSelectPage)
{
}

CFingerScan::CFingerScan(LPCTSTR pszCaption, CWnd* pParentWnd, UINT iSelectPage)
      :CPropertySheet(pszCaption, pParentWnd, iSelectPage)
{
      AddPage(&Setup);
}

CFingerScan::~CFingerScan()
{
}

And here's the property page class:
CSetupPage::CSetupPage() : CPropertyPage(CSetupPage::IDD)
{
      //{{AFX_DATA_INIT(CSetupPage)
            // NOTE: the ClassWizard will add member initialization here
      //}}AFX_DATA_INIT
}

CSetupPage::~CSetupPage()
{
}

void CSetupPage::DoDataExchange(CDataExchange* pDX)
{
      CPropertyPage::DoDataExchange(pDX);
      //{{AFX_DATA_MAP(CSetupPage)
            // NOTE: the ClassWizard will add DDX and DDV calls here
      //}}AFX_DATA_MAP
}


BEGIN_MESSAGE_MAP(CSetupPage, CPropertyPage)
      //{{AFX_MSG_MAP(CSetupPage)
            // NOTE: the ClassWizard will add message map macros here
      //}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CSetupPage message handlers

That's all, as you can see, is very simple, what is wrong with this code?

Thanks in advance