how to fix error c2065 in VS2003

I was compiling and encountered my 1 and only error.

error c2065: 'AhnHS_Callback' : undeclared identifier

Anyone can help me with this? I tried possible solutions, but still no luck for this. Hope someone can help me

int antihackNotFound = 0;
TCHAR    *pEnd = NULL;
TCHAR    szFullFileName[MAX_PATH] = { 0, };
TCHAR    szMsg[255];
int        nRet;
GetModuleFileName(NULL, szFullFileName, MAX_PATH);
pEnd = _tcsrchr( szFullFileName, _T('\\')) + 1;
if (!pEnd)
{
    return FALSE;    
}
*pEnd = _T('\0');
_stprintf(g_szIniPath, _T("%s"), szFullFileName);                
_stprintf(g_szHShieldPath, _T("%s\\HackShield"), szFullFileName);
_tcscat(szFullFileName, _T("HackShield\\EhSvc.dll"));            
_tcscat(g_szIniPath, _T("MiniAEnv.INI"));        
nRet = _AhnHS_Initialize(szFullFileName, AhnHS_Callback, 
    1000, "B228F2916A48AC24", AHNHS_CHKOPT_ALL|AHNHS_SELFDESTRUCTION_RATIO_FAST|
AHNHS_DISPLAY_HACKSHIELD_TRAYICON|AHNHS_CHKOPT_STANDALONE|
AHNHS_CHKOPT_LOADLIBRARY|AHNHS_CHKOPT_LOCAL_MEMORY_PROTECTION,
    AHNHS_SPEEDHACK_SENSING_RATIO_GAME);
if (nRet != HS_ERR_OK)
{
    _stprintf(szMsg, _T("HackShield Initialize Error. (Error Code = %x)."), nRet);
    MessageBox(szMsg, "GameSama.com", MB_OK);
    return FALSE;
}
nRet = _AhnHS_StartService();
assert(nRet != HS_ERR_NOT_INITIALIZED);
assert(nRet != HS_ERR_ALREADY_SERVICE_RUNNING);
if (nRet != HS_ERR_OK)
{
        _stprintf(szMsg, _T("HackShield Start Error. (Error Code = %x)."), nRet);
    MessageBox(szMsg, "GameSama.com", MB_OK);
    return FALSE;
}}

via Chebli Mohamed