Cannot read property 'x' of undefined using sprite.animations.play

[Archer3CL]

Im following this tutorial but im changing some of the sprites.

 

So, when the game is running, sporadically this error appears 

%c %c %c Phaser v2.0.7 | Pixi.js v1.6.1 | WebGL | WebAudio  %c %c  http://phaser.io  %c %c ♥%c♥%c♥  (03:01:25:504)  at public_html/js/phaser.js:22011Uncaught TypeError: Cannot read property 'x' of undefined (03:02:20:821 | error, javascript)    at Phaser.Sprite.setFrame (public_html/js/phaser.js:31278:33)    at Phaser.Animation.play (public_html/js/phaser.js:44089:22)    at Phaser.AnimationManager.play (public_html/js/phaser.js:43593:45)    at Neon.item.spawnEnemy (public_html/js/Game.js:61:26)    at Neon.Game.update (public_html/js/Game.js:43:23)    at Phaser.StateManager.update (public_html/js/phaser.js:16546:35)    at Phaser.Game.update (public_html/js/phaser.js:22122:24)    at Phaser.RequestAnimationFrame.updateRAF (public_html/js/phaser.js:38277:19)    at _onLoop (public_html/js/phaser.js:38263:30)> 

 

This is update

update: function() {        this._spawnRate += this.time.elapsed;        if (this._spawnRate > 1000) {            this._spawnRate = 0;            Neon.item.spawnEnemy(this);         }        this._enemyGroup.forEach(function(enemy) {            enemy.angle += enemy.rotateMe;        });        if (!Neon._lives) {            this.add.sprite((Neon.GAME_WIDTH - 594) / 2, (Neon.GAME_HEIGHT - 271) / 2, 'game-over');            this.game.paused = true;        }    }

This is spawnEnemy

spawnEnemy: function(game) {        var dropPos = Math.floor(Math.random() * Neon.GAME_WIDTH);        var dropOffset = [-27, -36, -38, -48];        var enemyType = Math.floor(Math.random() * 5);        var enemy = game.add.sprite(dropPos, dropOffset[enemyType], 'enemy');        enemy.animations.add('anim', [enemyType], 10, true);        enemy.animations.play('anim', 10, true);        game.physics.enable(enemy, Phaser.Physics.ARCADE);        enemy.checkWorldBounds = true;        enemy.events.onOutOfBounds.add(this.removeEnemy, this);        enemy.anchor.setTo(0.5, 0.5);        enemy.rotateMe = (Math.random() * 4) - 2;        game._enemyGroup.add(enemy);    },

And on my Preloader.js i declare my spritesheet like this

this.load.spritesheet('enemy', 'img/enemy.png', 50, 50);

My spritesheet is 200 x 50 and has 4 different sprites

 

The only thing i tried is to comment the error line on spawnEnemy but if i do that in the game only shows the first sprite.

 

Help is appreciated