No, access violation as i want.

As you suggest I change the code, now is that:

Code:
void WINAPI fxCriticalSection(void) {	
	while (TryEnterCriticalSection(&CriticalSection_Cadena) == 0) {		
		Sleep(Aleatorio(0,10));
		nHilosEsperan++;
	}

	char c = Aleatorio(97, 122); // del 97 al 122 las letras
	int nPos = Aleatorio(0, (MAXCADENA-1));	
	sCadena[nPos] = c;	
	nNumero = c;
	
	LeaveCriticalSection(&CriticalSection_Cadena);
}
It works fine.

Thank you for your suggest.

Best regards, Toño.