Error message is displayed when loading the Scrum or KanBan boards

An error is displayed when any of the KanBan or Scrum boards are selected and loaded into the browser.
If you clear the error message it is shown again when you click on a ticket to view it in the right hand (Jira Agile) pain.
Tickets can be viewed without issue in the issues tab (not in Jira Agile)
We tried restarting the Jira server which had no effect.
Our users are unable to start their next sprint as they cannot enter estimates in the Jira Agile interface. We therefore need this resolving as soon as possible.