That is unusual. Neither AE nor the render engine will launch?
What about the CC 2014 version, do they both still work?
Have you updated CC 2015 to version 13.5.1?
The CC 2014 still work.
I updated to 13.5.1.
I de-installed everything again and installed CC 2014 again.
Then installed CC2015 with the option to NOT delete CC 2014.
This has no effect. I still get the blank error window when I start AE or the render engine.
So I de-installed everything again, used the Adobe cleaner to completely remove everything including the CC desktop app.
Also de-installed every related AE plugin (Trapcode and Magic Bullet).
Rebooted the render node, installed CC desktop app again, installed AE CC 2014, upgraded to CC 2015, now with the option removing the former AE version.
Result, still nada. AE en the render engine keep starting with the blank error window.
When I click it away, AE starts normally, but I manually have to click the hidden OK button on the error window.
This sucks because it will halt the render node when AE is started by our rendermanager.
Well, that's certainly annoying. I can't imagine why you're getting a blank error message. There's obviously a reason for it, but I don't know what that is.
I'd recommend contacting Adobe support.
In the meantime, I'd recommend sticking with CC 2014 for your rendering. You can work in CC 2015 if you want to, AE CC 2014 will open files created in CC 2015 so, at render time, you can just use CC 2014 for the render. That's what I do anyway since CC 2014 has multiprocessing and CC 2015 doesn't.