dialog id undeclared identified

[dskp]

i have created win32 application with MFC in a shared Dll.

i have include a dialog with ID = IDD_DIALOG.i have created class for dialog which is CSettingsDlg derived from CDialog.
and included header

       class CSettingsDlg : public CDialog
{
	DECLARE_DYNAMIC(CSettingsDlg)

public:
	CSettingsDlg(CWnd* pParent = NULL);   // standard constructor
	virtual ~CSettingsDlg();

// Dialog Data
	enum { IDD = IDD_DIALOG1 };// error C2065: 'IDD_DIALOG1' : undeclared identifier

protected:
	virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support

	DECLARE_MESSAGE_MAP()
};

i am getting an error :
error C2065: 'IDD_DIALOG1' : undeclared identifier

what should i do ?