Luckily, my file created with C4D R13.0.5.1 still opens in R13.0.1.6. I just tried creating a test file. I created a camera with a few keyframes, a cube (converted to polys) with a few pos and rot keyframes and a spotlight. I applied the external compositing tag to the cube and clicked “solid” for good measure. I set my output options to all frames (0 to 90 default) and clicked Save .aec. Again, nothing is loaded into the After Effects project when I import the .aec file. Just to be sure, in Windows 7, the plugin should go in C:\Program Files\Adobe\Adobe After Effects CS5\Support Files\Plug-ins, right?