Error after re-starting HS3

[Looms01]

When I restart HS3, I get the following error in the logs:

• Initializing plug-in(1): Harmony Hub Interface: Error on InitIO: Object reference not set to an instance of an object

And I see this message in the plugin section

• Unable to start plug-in API: Only one usage of each socket address (protocol/network address/port) is normally permitted

Any ideas?