Error removing child

Hi i got some error when removing sprites from layer

i have an enemy object that is added every 3 sec

void HelloWorld::spawnEnemy()
{
enemyObj = new Enemy();
actionLayer~~>addChild;
}
and a method to remove it
void HelloWorld::removeSprite
{
actionLayer~~>removeChild(sprite, true);
}

i call the remove sprite from my enemy object
parentLayer->removeSprite(this);

why when i call that method suddenly my apps is closed
help plz
thanks