Mavros not arming quadcopter?

edit

Hi,

I've been trying to use mavros ( http://wiki.ros.org/mavros ) to fly a 3DR Iris quadcopter that has a Pixhawk on it, but we're having trouble arming the system.

Run through of the scenario:

1. We're inside, plug the battery in for the quadcopter, and the quad goes to flashing blue. This stands for "Autopilot ready but no GPS lock". We can arm the quadcopter with the RC controller at this point.
2. We plug in the radio modem and run 'roslaunch mavros apm2_planner.launch'. At this point we are connected to the quadcopter. When we rostopic echo the /mavros/battery and /mavros/imu/raw_data topics (among others) we get good data. We can pull and push missions.
3. We put the RC controller in AUTO mode

4. We run 'rosservice call /mavros/cmd/arming true' in a new terminal, it returns

   success: false

   result: 3

Does anyone have any ideas? Do we need to be outside with GPS fix? Are there any flags that need to be satisfied in the code before it will allow arming?

Thanks