"wtf, why?!"
Thanks to the autor of this reddit-post:

This error seems to appear only on Mac. It means, that some DRM-stuff is broken and needs to be recreated.


  1. Boot into recovery (CMD+R)
  2. Open the built-in terminal and type in the command EXACTLY as written:

nvram 8be4df61-93ca-11d2-aa0d-00e098032b8c:epid_provisioned=%01%00%00%00

  1. press Return
  2. type in reboot and press Return again

Now everything should work again.