You are not providing any system information or other details nor describing properly what you think your C4D is doing wrong. nobody can help you on vague "This doesn't work." statements.
That sounds like an admonishmenrt... I was diverted here from online chat, so thought I was opening discussion. Here's more detail.
Machine: Asus G750J (Haswell with 16 Gig Ram) and an NVidia GeForce graphics card.
Operating System: Windows 8.1
I have Creative Cloud Membership.
I tried uninstalling and reinstalling After Effects after the problem happened, but the same issue is there.
After Effects is installed at the default location which is:
C:\Program FIles\Adobe\After Effects CC
What version of CC are you running?
What are you trying to do when it gives you the error?
Have you rebooted your computer?
What version of CC?After Effects CC 188.8.131.52
I was in After Effects, and clicked FIle->New->MAXON Cinema 4D File...
I have rebooted the computer a few times. I have also uninstalled and reinstalled After Effects once.
I am hoping that there is someway to reinstall the plug-in, or if it is installed, but somehow disabled, to re-enable it.
The C4D install not being found probably means that you have mundane user privilege/ file permission issues or e.g. your virus scanner is blkocking communication with the extern C4D process from within the AE host plug-in. Turn that stuff off and run with sufficient user privileges. The rest is neither here nor there. I know you're gonna hate me for it but as per your own words "buttons don't do the right thing, there must be some initialization step I'm missing" doesn't really strike me like you even bothered to read the help. The least you could do is tell us what buttons you actually pushed. The default UI layout even in teh stripped down version that C4D Lite is has something like 120 visible icons/ buttons... Really nothing personal, but you would do good to at least look up some basic C4D tutorials. The buttons most likely do what they always have done, but you are using them in the wrong way or expect something that they can't do.
I'll come back in a few hours to re-address the buttons issue. For now, I would like to resolve the sudden change that makes it so that I cannot start C4D any more. I was using it. Permissions did not change. It is not an access issue. I did watch all of the video tutorials, and it was in trying to reproduce the steps in the video that this change happened. I got one video created with an animated object (text) moving with the background... and while trying to do a second one, I started getting this error.
Once I can connect to C4D again, I will take some screen shots to try and explain the button issue.
If in the mean time, you can suggest other documentation or tutorials than the ones on the Adobe site for C4D, I will happily watch them.
Just as a followup, I spoke to Mylenium on the phone, and he was successful in helping solve both of my problems... We still don't know why it worked previously and then stopped, but that's not an issue. What made all the difference was setting AE to run as administrator (not my account with admin privilege). He also showed my what I was doing wrong on the C4D button clicks... and the official tutorials for C4D. I'm a beginner, but I'm good to go!