Check for updates using Help > Updates to see if there are any other pending updates for your software. If there are, install those.
Then, restart your computer and try again to install the manual update for After Effects CC (12.0.1) for Mavericks.
Be sure that you're not running After Effects as a trial. Be sure that you have signed in and that the software is activated.
Are you using a free trial version of After Effects CC (12.0)? This update will only work if you are signed in, using an activated version of After Effects CC (12.0), as explained here:
"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. Sign in to Creative Cloud using any Adobe Creative Cloud application on your computer to activate all Adobe Creative Cloud applications on that computer."
> So what you're saying is there is no way to use the trial version of After Effects CC with Mavericks?
For now, yes.
The After Effects CC (12.1) update due out next week will be applicable to the trial version, and it includes the same fix for Mavericks compatibility, plus much more:
Do you know what day this week the update for the trial version will be available?
In October, as stated here:
Will all the work done on After Effects before updating to OS X 10.9 still be accessible?