Mavericks broke a lot of things including AE.
However, the day Mavericks was released to the public, Adobe released an update that made AE work again. Download the update and all will be well. After Effects CC (12.2.1) bug-fix update
Not only does that include the 12.0.1 Mavericks fix, but 12.1 and 12.2 both included some great new features.