tween alpha - Flash not working

Hello,

I use a tween effekt, to see an Hotspot-Image. HTML5 works, but flash doesn't.

tween(hotspot[get(hotspot_name_img)].alpha, 0, 0.5);

btw.

tween(hotspot[get(hotspot_name_img)].alpha, 1, 0.5);

With HTML5 everything is fine, but the flash player don't shows this effect.

What's wrong?

Best regards
canrin