There are two types of machines in Orchestrator. Standard and Template.
Standard: Is intended per host, although when you configure the Robot there is nothing stopping you from referencing the same machine key, but I believe the behaviour would be the first host to connect with a matching machine name will get the registration while the second one (assuming the machine name is the same) will be rejected. Standard machines at this time are used for unattended and attended type robots.
Templates on the other hand are used when the name of the host will not be consistent or you have a group of machines to connect. They are used in conjunction of Attended Robots (Attended / Studio)
Hover your mouse over the status message and it will reveal a more details indication of what the problem is. Alternatively, look in your Event Viewer > Windows Logs > Applications.