The target computer is offline and the system's Offline Settings prevents deployment to offline computers.
A computer's offline status is determined by ping (ICMP echo). If the computer is online but not responding to pings it will be treated as though it is offline.
Correct the issue preventing the pings from responding (such as a firewall) or change the Offline Settings (File > Preferences > Deployments) to allow use Ping for Offline Testing or Send Wake-on-LAN to Offline Computers.
Available Offline Settings: