There are a bunch of threads on this subject. You have to download the latest CS6 build from Adobe and install that for it to work.
Rick is right. You need After Effects 11.0.4 or it will not run.
There are also some issues running that old of a version on El Capitan. Some minor playback issues (you'll need to let the RAM preview loop to get proper playback) and motion sketch problems. Some info here: After Effects and Character Animator ready for Mac OS X v10.11 (El Capitan)