hi all i run hector quadrotor package but in my case indoor and outdoor packages run without quadrotor and rviz does not show any picture from camera,when i run

$source ... $roslaunch hectorquadrotorgazebo quadrotoremptyworld.launch i see this error

while processing /home/masoud/hectorquadrotortuturial/hectorquadrotor/hector quadrotor gazebo/launch/spawnquadrotor.launch: Invalid tag:Cannot load command parametr [robotdescription]: command [/opt/ros/groovy/stacks/xacro/xacro.py '/home/masoud/hectorquadrotortutorial/hectorquadrotor/hectorquadrotorurdf/quadrotor.gazebo.xacro'] returned with code [1].

Param xml is