Your pc should have got all the updates that are fixing the activation problems. As far as we experienced with our test machines, your will have to reboot your pc 2 times to get all the patches applied.
After that you should finally able to get rid of the error and see the usual activation page from Microsoft.
I’ll be off of office until next Monday, please get in contact with Fabio in mail-cc or Claudio via ticket (you already raised) if your problem won’t be solved. In this case my suggestion is to roll back to office 2013 until we will find a solution for all the strange issues this package is having.
I’m really sorry for the waste of time you had … I can only say thanks for your troubleshooting that helped us to find a possible solution.