saveFrame("/sdcard/img-###.png") fails to be executed at Android Application

Hello dudes,

I am a newbie in using the Processing Language. I have developed a small application which displays randomly circles on the phone screen. Their radius is also one of the first 20 fibonacci numbers in magnitude. I have added a mousePressed() event in order to save my creations. However, my app closes instantly when I touch the screen with my finger. Can you help me in order to solve this problem?

My code:

void setup() {
 size(displayWidth,displayHeight);
 smooth();
 background(random(255),random(255),random(255));

}


void draw() {
  noFill();
  stroke(255);
  strokeWeight(4);
  for(int i=0; i<20; i++) {
    ellipse(random(width),random(height),fibonacci(i)/5,fibonacci(i)/5);
    delay(10);
  }


}

int fibonacci(int n) {
 if (n==0 || n==1) {
  return 1;
 }
 return fibonacci(n-1)+fibonacci(n-2);

}

void mousePressed() {
   saveFrame("/sdcard/img-####.png");
 }


void delay(int ms)
{
   try
  {
    Thread.sleep(ms);
  }
  catch(Exception e){}
}

The Android API I am using is the one recommended by the Processing Wiki.

Thanks in advance!