This is often due to permissions or account privileges or security concerns. On Windows machines, this error is usually solved by running AE as an administrator. I'm not sure the Mac equivalent, but you could certainly make sure that permissions are set correctly: fixing permissions problem
Having them right will prevent other issues in the future.
Your difficulty is likely in the internal security or TCP settings. From the bottom of this Adobe blog post:
Depending on your computer’s security settings, you may see some warnings about TCP communication; this is because After Effects and the background CINEMA 4D renderer are communicating using TCP, which some security software may interpret as dangerous malware communication. For example, Mac OS will ask you to confirm if you want to run this software “downloaded from the Internet”. Go ahead and accept the communication between these applications. If you can import a .c4d file, but it fails to render, check your security settings to see if Mac OS Gatekeeper or your firewall are blocking the background CINEMA 4D renderer from functioning and communicating with After Effects. In Mac OS, check the General tab of the Security & Privacy system preferences, and make sure that Allow Applications Downloaded From is set to Anywhere. (Note that the TCP port used is defined in the Options in the CINEWARE effect, and the choice is stored in the After Effects preferences file.)
One user on the CreativeCOW said,
Go to the Effects Control panel and click on Cineware Options
Under CINEWARE TCP PORT mine was set to 5030 and I changed it to 5027, and now I can see my CD4 layer in AE
Hopefully one of these things solves it for you.
Sorry guys neither of these things help. For some reason there is no Cinema 4D installation on my machine and I dont think its a TCP thing or a security thing: it just doesnt install when I install After Effects.
I'd suggest uninstalling, running the Adobe CC Cleaner, and reinstalling.