Q7620035: We're trying to get the action "Reboot this server after failure" to restart a computer on the network and it's not working. Network Monitor logs the following error: "Reboot Server command is NOT sent to computer, error=[Unable to initiate a shutdown]"
Try the SHUTDOWN utility (part of the Windows Resource Kit) to reboot that machine, using the same credentials as the Network Monitor service. Check the error. Most probably, the service account has no administrative privileges on the remote computer.