RLException: unable to launch error while roslaunch

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            <?xml version="1.0"?>

<launch>

  <include file="$(find opencv_detector)/launch/facedetector.launch">
    <arg name="image_topic" value="/vrep/image" />
  </include>

  <!--START KEY TELEOP-->
  <node pkg="teleop_twist_keyboard" type="teleop_twist_keyboard.py" name="teleop">
    <remap from="/cmd_vel" to="/vrep/cmd_vel"/>
  </node>

  <node pkg="rviz" type="rviz" name="rviz" args="-d $(find demo_elec3210)/sample.rviz"/>

  <arg name="tf_map_scanmatch_transform_frame_name" default="scanmatcher_frame"/>
  <arg name="base_frame" default="base_link"/>
  <arg name="odom_frame" default="nav"/>
  <arg name="laser_frame" default="laser_link"/>
  <arg name="camera_frame" default="camera_link"/>
  <arg name="pub_map_odom_transform" default="true"/>
  <arg name="scan_subscriber_queue_size" default="5"/>
  <arg name="scan_topic" default="vrep/scan"/>
  <arg name="map_size" default="1024"/>

  <node pkg="hector_mapping" type="hector_mapping" name="hector_mapping" output="screen">

    <!-- Frame names -->
    <param name="map_frame" value="map" />
    <param name="base_frame" value="$(arg base_frame)" />
    <param name="odom_frame" value="$(arg odom_frame)" />
    <param name="odom_frame" value="$(arg laser_frame)" />
    <param name="odom_frame" value="$(arg camera_frame)" />

    <!-- Tf use -->
    <param name="use_tf_scan_transformation" value="true"/>
    <param name="use_tf_pose_start_estimate" value="false"/>
    <param name="pub_map_odom_transform" value="$(arg pub_map_odom_transform)"/>

    <!-- Map size / start point -->
    <param name="map_resolution" value="0.050"/>
    <param name="map_size" value="$(arg map_size)"/>
    <param name="map_start_x" value="0.5"/>
    <param name="map_start_y" value="0.5" />
    <param name="map_multi_res_levels" value="2" />

    <!-- Map update parameters -->
    <param name="update_factor_free" value="0.4"/>
    <param name="update_factor_occupied" value="0.9" />    
    <param name="map_update_distance_thresh" value="0.4"/>
    <param name="map_update_angle_thresh" value="0.06" />
    <param name="laser_z_min_value" value = "-1.0" />
    <param name="laser_z_max_value" value = "1.0" />

    <!-- Advertising config --> 
    <param name="advertise_map_service" value="true"/>

    <param name="scan_subscriber_queue_size" value="$(arg scan_subscriber_queue_size)"/>
    <param name="scan_topic" value="$(arg scan_topic)"/>

    <param name="tf_map_scanmatch_transform_frame_name" value="$(arg tf_map_scanmatch_transform_frame_name)" />
  </node>

  <node pkg="tf" type="static_transform_publisher" name="world2map_broadcaster" args="0 0 0 0 0 0 world map 100"/>
  <node pkg="tf" type="static_transform_publisher" name="map2nav_broadcaster" args="0 0 0 0 0 0 map nav 100"/>
  <node pkg="tf" type="static_transform_publisher" name="nav2base_broadcaster" args="0 0 0 0 0 0 nav base_link 100"/>
  <node pkg="tf" type="static_transform_publisher" name="base2laser_broadcaster" args="0 0 0 0 0 0 base_link laser_link 100"/>
  <node pkg="tf" type="static_transform_publisher" name="base2camera_broadcaster" args="0 0 0 0 0 0 base_link camera_link 100"/>

  <node pkg="detection_msgs" type="patch_visualizer" name="face_visualizer" output="screen">
    <remap from="camera" to="/vrep/image" />
    <remap from="detections" to="/facedetector/faces" />
    <param name="cleanup_delay" value="0" />
  </node>

</launch>

This is my launch file and I am trying to run it via roslaunch opencv_detector facedetector.launch where this is the python code for opencv_detector

#!/usr/bin python3

import roslib
roslib.load_manifest('opencv_detector')
import rospy
import sys, select, termios, tty
import time
import Image
import os
import cv2
from std_msgs.msg import String
from std_msgs.msg import Bool
import sensor_msgs.msg
from dynamic_reconfigure.server import Server as DynamicReconfigureServer
from detection_msgs ...