NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.7

This is part of the sketch I am using:

#include <NewPing.h>

NewPing sonar = NewPing(A4, A4, 300);

void setup() {
}

void loop() {
  tone(12, 2999, 3000);
}

When I try to verify the sketch I always get this error:

core.a(Tone.cpp.o): In function `__vector_7':
C:\...\arduino-1.0\hardware\arduino\cores\arduino/Tone.cpp:523: multiple definition of `__vector_7'
NewPing\NewPing.cpp.o:C:\...\Documents\Arduino\libraries\NewPing/NewPing.cpp:214: first defined here

Even when I comment out or delete the 3rd line ("NewPing sonar = ...") I still get the same error.

basile

P.S.: I am using a Parallax PING))) sensor on an Arduino UNO board and I think (I am not sure because the test has been performed by a friend) that when it is connected to A4 (as in the example) it doesn't work. Unfortunately right now there are no digital ports available.