That's a QT error coming from Autodesk Licensing (which uses QT for the user interface).
Render process exited with code: 11
Do you want to reload the page?
I would close down all applications and then try running just the Arnold License Manager from a terminal:
/Applications/Maxon\ Cinema\ 4D\ R25/arnold/bin/ArnoldLicenseManager.app/Contents/MacOS/ArnoldLicenseManager
After that, I would also ask over at the Autodesk Installation and Licensing forum:
https://forums.autodesk.com/t5/installation-licensing/bd-p/24
Please provide the details of your OS and machine
// Stephen Blair
// Arnold Renderer Support
