Sky Shere does not work on android

Hello,

I’m trying to add as sky sphere in my game using the following code:
[java] Texture tex = _assetManager.loadTexture(“Textures/Skysphere.jpg”);
_rootNode.attachChild(SkyFactory.createSky(
_assetManager, tex,Vector3f.UNIT_XYZ, true, 500));
_cam.setFrustumFar(1000.0f);[/java]

it works fine on my PC, but nothing is displayed on my android device!
Any idea?