To avoid random null-pointer errors, better use:
Code:
action coffre()
{
        while(!player) { wait(1); } // wait till player pointer becomes valid

	while(me)
	{
		if(vec_dist(my.x,player.x) < 100)// Quand le jouer est près
		{
			//event
		}
		wait(1);
	}
}