To start, go to that "About After Effects" selection and tell us about the precise -- down to the last decmial point -- version of AE you're trying to run.
Then go to your "About This Mac" selection and tell us about your precise -- down to the last decimal point -- version of your Mac OS.
That'll get the ball rolling.
After Effects version = 18.104.22.168
OSX Yosemite version = 10.10.1