I have no idea what gives. I don't have Final Cut Pro, and my videos retain the alpha matte, so I don't need to work with still-image TIFFs. Some of my fellow videots over in the Director's Cut forum make use of the software, so maybe they'll know if it's a software-specific issue. Try asking wolf359 or intercept789. But if you can't figure it out, you can try importing the live-action into Poser as a background video, and effectively do the compositing while you render. Just make sure the frame-sizes/frame-rates match.