Can't roslaunch pi_tracker skeleton.launch

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Hello, Im trying to use the pirobot's pi_tracker. Im not sure my catkin_make is done or not but it showed 100%, so i assumed it's done. But when i try to roslaunch pi_tracker skeleton.launch, this is the result anybody can give some advice about this? thanks

mob17@Seguro:~/ros_ws$ roslaunch pi_tracker skeleton.launch
... logging to /home/mob17/.ros/log/ea684000-96e6-11e8-8192-3476c54e4047/roslaunch-Seguro-8538.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
WARNING: disk usage in log directory [/home/mob17/.ros/log] is over 1GB.
It's recommended that you use the 'rosclean' command.

Traceback (most recent call last):
  File "/opt/ros/indigo/share/xacro/xacro.py", line 62, in <module>
    xacro.main()
  File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 687, in main
    process_includes(doc, os.path.dirname(args[0]))
  File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 246, in process_includes
    filename_spec = eval_text(elt.getAttribute('filename'), {})
  File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 485, in eval_text
    results.append(handle_extension(lex.next()[1][2:-1]))
  File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 473, in handle_extension
    return eval_extension("$(%s)" % s)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 66, in eval_extension
    return substitution_args.resolve_args(str, context=substitution_args_context, resolve_anon=False)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 316, in resolve_args
    resolved = _resolve_args(resolved, context, resolve_anon, commands)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 329, in _resolve_args
    resolved = commands[command](resolved, a, args, context)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 157, in _find
    pkg_path = rp.get_path(args[0])
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 203, in get_path
    raise ResourceNotFound(name, ros_paths=self._ros_paths)
rospkg.common.ResourceNotFound: rbx2_description
ROS path [0]=/opt/ros/indigo/share/ros
ROS path [1]=/home/mob17/ros_ws/src
ROS path [2]=/home/mob17/kentac_ws/src
ROS path [3]=/opt/ros/indigo/share
ROS path [4]=/opt/ros/indigo/stacks
Invalid <param> tag: Cannot load command parameter [robot_description]: command [/opt/ros/indigo/share/xacro/xacro.py '/home/mob17/ros_ws/src/pi_tracker-indigo-devel/urdf/pi_robot/pi_robot_with_two_arms.xacro'] returned with code [1]. 

Param xml is <param command="$(find xacro)/xacro.py '$(find pi_tracker)/urdf/pi_robot/pi_robot_with_two_arms.xacro'" name="robot_description"/>
The traceback for the exception was written to the log file