GPS prearm errors when arming in SITL mode

Hi, I’m running ArduCopter 4.1 on a black cube through MaxProxy and AirSim. When I issue the command “arm throttle” I get the following response:

Got COMMAND_ACK: COMPONENT_ARM_DISARM: FAILED
AP: PreArm: GPS 1: not healthy
AP: PreArm: GPS 1: not healthy

This is on running on a Windows 10 machine. Parameters were taken from Tools/autotest/default_params/copter.param.