Can't connect to Agents

I've set up my load test which works fine in local mode with a VU scenario (using load ui 2.0.2)

I've created agents which I've deployed the VU scenario to.
But when I run the test nothing happens and the agent looks like it is still trying to connect.
When I look in system log there is a message saying 'unable to find valid certification path to requested target.'

Anyone know what the solution is?