how to delete failed message

In the Neuron Explorer's Failed Messages overview, we want to delete a single message from the failed messages database. When opening a failed message and right clicking on the message, Delete in the drop down list is dimmed out (se attached file). We run as local administrator on the server. And we do have rights to click Delete All from the main window. Can you please explain how to enable deleting a single failed message. We use Neuron 3.1.0.413.

Regards,

Nanna Fog