[angular-cli] Error: Local workspace file ('angular.json') could not be found

I had the same problem and found that there was no package.json in my project (but only the package-lock.json). I then

  1. restored the package.json from source control
  2. uninstalled the global and local angular-cli versions (like the instruction says)
  3. followed the standard upgrade procedure

..and all worked out fine. Took a while to figure it out, but that did it for me.