I found the solution for you.
RUN secpol.msc in CMD (on the computer u want to enable the remote shutdown)
Go to Local Policies -> User Rights Assignment and search for "Force shutdown from a remote system"
Double click it and then "Add User or Group..." and type "Everyone" and then add it.
This SHOULD work! I've set this configuration on my computer and then executed this command on my brother's PC while we are on the same LAN network and i've got the shutdown message AND the computer did restart.
shutdown -m \\mypcname -r -c "this pc will shutdown in 60 secs" -t 60
Be sure that u can see the computer u want to shutdown trought net view. But u already see it, because u are getting the Access denied. (5).
Report back to the question if it works!
Kind Regards