Who needs a Software Real Time Clock?

Hello everybody.
I'm using version 0012 with DateTime libraries. The following code doesn't run but if I comment "#include DateTimeStrings" everything is ok.

#include <DateTime.h>
#include <DateTimeStrings.h>

void setup(){
Serial.begin(9600);
}

void loop(){
Serial.print("ciao bello...");
}

I look at the C++ code but it seems ok! What happen???