PS2Mouse library breaks serial monitor output

Other Hardware Sensors
1

I am trying to read a PS2 mouse movements with arduino.

But I discovered that PS2Mouse initialization breaks serial monitor output (no output at all)

This is the code that produces the behaviour:

#include <PS2Mouse.h>
#define MOUSE_DATA 5
#define MOUSE_CLOCK 6
PS2Mouse mouse(MOUSE_CLOCK, MOUSE_DATA, STREAM);

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

void loop() {
  Serial.println("A");
}

The "A" is never shown in Serial monitor. But if I remove the following line:

mouse.initialize();

then serial monitor backs to life...

What can be wrong?