How to run robot test cases in a headless box. [Bamboo] [RobotFramework]

I've set up a VM box ubuntu and Bamboo server to control build and integration tests to an application.

I can run (manually or even trough Bamboo) the test cases WHILE I'm connected to the VM and see all the selenium magic happening.

However when the VM is started as headless and I try to run the test cases I get the error below for all test cases:

WebDriverException: Message: The browser appears to have exited before we could connect. If you specified a log_file in the FirefoxBinary constructor, check it for details.

Any good tip or ideas to run it in headless mode?

Cheers