Question: 

I have just imported data from a Zendesk helpdesk. Now I can only see the Agents screen in the admin interface. When I log out, I see a 'License Error' message even though my license has not expired.

Answer:

The import process adds some types of Zendesk accounts (like light-agents) as Deskpro agents, so you may have ended up with more agents than you expected. This is causing you to exceed the number of agents authorized by your license. Delete the extra agent accounts to fix the problem.