ResourceNotFound: gazebo_ros Issue

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I'm using: Ubuntu 16.04.7 LTS along with Gazebo multi-robot simulator, version 7.16.1 to lunch the simple arm robot from https://github.com/udacity/RoboND-sim... I can initiate and build my project, but when I run the following command:

$ roslaunch simple_arm robot_spawn.launch

I get the following error which seems to be an issue with catkin not finding my gazebo:

    Traceback (most recent call last):
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/__init__.py", line 308, in main
        p.start()
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 268, in start
        self._start_infrastructure()
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 217, in _start_infrastructure
        self._load_config()
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/parent.py", line 132, in _load_config
        roslaunch_strs=self.roslaunch_strs, verbose=self.verbose)
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/config.py", line 451, in load_config_default
        loader.load(f, config, verbose=verbose)
      File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 750, i

n load
    self._load_launch(launch, ros_config, is_core=core, filename=filename, argv=argv, verbose=verbose)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 722, in _load_launch
    self._recurse_load(ros_config, launch.childNodes, self.root_context, None, is_core, verbose)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 686, in _recurse_load
    val = self._include_tag(tag, context, ros_config, default_machine, is_core, verbose)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 95, in call
    return f(*args, **kwds)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 589, in _include_tag
    inc_filename = self.resolve_args(tag.attributes['file'].value, context)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/xmlloader.py", line 183, in resolve_args
    return substitution_args.resolve_args(args, context=context.resolve_dict, resolve_anon=self.resolve_anon)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 370, in resolve_args
    resolved = _resolve_args(resolved, context, resolve_anon, commands)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 383, in _resolve_args
    resolved = commands[command](resolved, a, args, context)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 151, in _find
    source_path_to_packages=source_path_to_packages)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/substitution_args.py", line 197, in _find_executable
    full_path = _get_executable_path(rp.get_path(args[0]), path)
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 207, in get_path
    raise ResourceNotFound(name, ros_paths=self._ros_paths)
ResourceNotFound: gazebo_ros
ROS path [0]=/opt/ros/kinetic/share/ros
ROS path [1]=/home/liam/workspace/catkin_ws/src
ROS path [2]=/opt/ros/kinetic/share

Is there anything I'm missing? I appreciate your time and help!