hi looking for help with this code

Code:
onClipEvent (load) {
	power = 1;
	yspeed = 0;
	xspeed = 0;
	friction = 0.95;
	gravity = 0.1;
	thrust = 0.75;
	radius = 10;
}
onClipEvent (enterFrame) {
	xspeed *= friction;
	yspeed += gravity;
	_y += yspeed;
	_x += xspeed;
	if (Key.isDown(Key.LEFT)) {
		xspeed -= power;
	}
	if (Key.isDown(Key.RIGHT)) {
		xspeed += power;
	}
	if (Key.isDown(Key.UP)) {
		yspeed -= power*thrust;
	}
	if (Key.isDown(Key.DOWN)) {
		yspeed += power*thrust;
	}
	if (Key.isDown(Key.SPACE)) {
		_root.player.player_beaming.gotoAndStop(2);
	} else {
		_root.player.player_beaming.gotoAndStop(1);
	}
	while (_root.world1_1_walls.hitTest(_x, _y+radius, true)) {
		_y--;
	}
	while (_root.world1_1_walls.hitTest(_x, _y-radius, true)) {
		_y++;
	}
	while (_root.world1_1_walls.hitTest(_x-radius, _y, true)) {
		_x++;
	}
	while (_root.world1_1_walls.hitTest(_x+radius, _y, true)) {
		_x--;
	}
}
the above code works fine, but but when my player hits the wall in certain places it seems to remove the player movie clip... can someone please help?