Problems with Raytrace and Alphamap

Recently I tried to make a 2D-Character animateable in blender. But up to now I have only the head- and eyetexture on planes because I have a problem with the rendersettings. I want to use ambient occlusion with raytrace. When I use this settings blender renders shadow of a texture with alphamaps it renders the shadow of the plane and ignores the alphamap.

Does anybody know wich settings I have to use? To enable TraSha in the Shaders Panel do not affect anything with enabled rytrace.