A permissions issue occurred which prevented the target computer from being shutdown.
It may be that the credentials don't have sufficient privileges to shutdown the computer (i.e. not an Administrator) but more likely it's that Windows has a separate policy for remote shutdown permissions which has been restricted or disabled.
Enable remote shutdown on the target computer by editing its security policy or by changing a GPO.
Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignment > Force shutdown from a remote system