Install the After Effects CC (12.0.1) update for Mac OS X v10.9 (Mavericks):
Be sure that you are signed in and have activated the software—i.e., ensure that you are not running After Effects in free trial mode. The update will not work if you are running the application in trial mode.
This update is only available as a manual download (not through the Creative Cloud automatic update mechanism) to prevent users on versions of Mac OS X other than v10.9 (Mavericks) from installing it unnecessarily.
Adobe After Effects CS6 (11.0.3) was released a little while ago with this fix, plus fixes for many other crashes and bugs. Details: http://adobe.ly/AE_CS6_1103
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