Hi Borislav.
Here is the full code:

VC++

#include "stdafx.h"
#include "pro_ext.h"

// http://msdn.microsoft.com/en-us/library/windows/desktop/ms679347%28v=vs.85%29.aspx
void vfpFlashWindowEx (ParamBlk *parm)
{
HWND hWnd;
if (parm->p[0].val.ev_long==0)
{
hWnd = _WhToHwnd(_WMainWindow());
}
else
{
hWnd = _WhToHwnd(parm->p[0].val.ev_long);
}

FLASHWINFO info;
info.cbSize = sizeof(info);
info.hwnd = hWnd;
info.dwFlags = FLASHW_ALL;
info.dwTimeout = 0;
info.uCount = parm->p[1].val.ev_long;

_RetInt(FlashWindowEx(&info), 10);
}

FoxInfo myFoxInfo[] =
{
{"VFPFLASHWINDOWEX", (FPFI) vfpFlashWindowEx, 2, "I,I"},
};

extern "C" FoxTable _FoxTable =
{
(FoxTable *)0, sizeof(myFoxInfo)/sizeof(FoxInfo), myFoxInfo
};

VFP:

Set Library To VisualFoxProFLL.fll

Local lnHwnd
m.lnHwnd = 0
Try
Messagebox(vfpFlashWindowEx(m.lnHwnd,3))
Catch
Throw
Finally
Release Library VisualFoxProFLL.fll
Endtry

Return

I don't know how to debug... : (