using alpha channel in after effects

i searched the archives on this and still couldnt resolve my problem. hopefully someone can help me out. i have a very simple animation. im using a plane and having it deform along a circle spline using the path deformer plug-in. there are no background scenes and i have checked Alpha Channel and Straight Alpha in render settings.

When i import this rendered movie into after effects and place it above another video, the bottom video does not show through. I tried going into the Interpret Footage menu for my cinema 4d animation in after effects, but the alpha section is all grayed out.

I appreciate any help!
-vikas-