rosrun执行python报错

请教大家一个问题： 执行rosrun mrobot_navigation random_navigation.py, 一直报错permission denied，   已经给random_navigation.py授权了，还是报同样的错，单独执行 python random_navigation.py，是不会报错的，rosrun执行就会报错，这是怎么回事，  random_navigation.py部分代码如下：

#!/usr/bin python
# -*- coding: utf-8 -*-

import roslib;
import rospy
import actionlib
from actionlib_msgs.msg import *
from geometry_msgs.msg import Pose, PoseWithCovarianceStamped, Point, Quaternion, Twist
from move_base_msgs.msg import MoveBaseAction, MoveBaseGoal
from random import sample
from math import pow, sqrt

class NavTest():
    def __init__(self):