After the latest Windows 10 update, the procedure described in Conclusively stop wake timers from waking Windows 10 desktop no longer works. When attempting to save changes to the reboot task conditions, the user is asked to supply a password for account S-1-5-18, which is unknown. Taking ownership of the "reboot" file doesn't help. Can someone please supply an updated procedure? Thanks.
S-1-5-18 is the Local System account so it is not sufficient to be Admin to change taskschd for reboot for UpdateOrchestrator.
You can solve it by running as local system using tools like PsExec from SysInternals. Download sysinternals PSTools and run this command in an elevated command prompt (as administrator) to launch Task Scheduler:
psexec -i -d -s mmc taskschd.msc