Note: You are currently viewing documentation for Moodle 2.8. Up-to-date documentation for the latest stable version of Moodle may be available here: error/local hub/cannotregisternotavailablesite.
To register with a hub your Moodle site needs to be accessible by the hub so the two can communicate with one another.
The error indicates that the hub could not reach your site.
Reasons why you may have seen this error: