did the excercise twice, even restarted the whole server after configuring the regkey, validated that the value of AIAssistantDisabled is indeed "1" , and that it is a reg dword 32bit, in the correct regkey location
Maybe just a random idea, are you connecting with a remote console? Could you maybe try to add the key not only on the backup server but on the computer where you have opened the console (eg your laptop)