I can't use FindWindowEx() to find control.

[mmc01]

I want to open Microsoft Security Essential program and click Scan now button with VC . I can find window but Can't find control. This is my code when I run this code it show Control not found . I try to test this code with click Browse button in Run program it work but when I try to use with Microsoft Security Essential it not found control. I don't know why maybe this control is in Tab . How to use FindWindowEx() click Scan now button in Microsoft Security Essential ?

int run_ms(){	

	ShellExecute(NULL, L"open", L"C:/Program Files/Microsoft Security Client/msseces.exe", NULL, NULL, SW_SHOWNORMAL);

        HWND w;
	w=FindWindow(NULL, L"Microsoft Security Essentials");

		if(w==NULL)
				MessageBox(NULL,L"Not found",L"",MB_OK);

		else{
				HWND cb;
				cb = FindWindowEx(w,NULL,NULL,_T("&Scan now"));		

			if(cb!=NULL)
			{
				SendMessage(cb,WM_LBUTTONDOWN, NULL,NULL);
				SendMessage(cb,WM_LBUTTONUP, NULL,NULL);
			}
			else
				MessageBox(NULL,L"Control not found",L"",MB_OK);
		}

			return 0;
}