Problems with AO and animated textured Alpha

Hi everyone,

I’m kind of in trouble here. I am working on an animation, and I have a lil big problem.

I have a ring, this ring is around a sphere. I animated the texture of the ring so that it gradually appears (not all at once). I made this using a highly contrasted “blend” texture, and modified it’s offset so that it moves. This texture add to the material’s alpha (this means, the material’s alpha is 0.0). Making the object gradually appear.

The problem is that AO doesn’t recognize this alpha, and it casts a big bad shadow around the sphere, even when the texture hasn’t even started to move, and the right is completely transparent! I first thought I didn’t set up the materials correctly, but after cheking with lamps, I saw that using ray based shadows, the transparent parts of the ring dont cast a shadow.

This is, AO for some reason, simply doesn’t like alpha modified by a texture, is there some kind of workaround for this? Thanks!