catkin_make error permissions on external drive

edit

I am trying to create catkin workspace on a external drive and I am getting the following error when I run catlkin_make

` File "/usr/lib/python2.7/subprocess.py", line 566, in check_output
    process = Popen(stdout=PIPE, *popenargs, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child
    raise child_exception
OSError: [Errno 13] Permission denied
CMake Error at /opt/ros/indigo/share/catkin/cmake/safe_execute_process.cmake:11 (message):
  execute_process(/usr/bin/python
  "/media/nathaniel/Data/catkin/build/catkin_generated/generate_cached_setup.py")
  returned error code 1
Call Stack (most recent call first):
  /opt/ros/indigo/share/catkin/cmake/all.cmake:186 (safe_execute_process)
  /opt/ros/indigo/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:52 (find_package)


-- Configuring incomplete, errors occurred!
See also "/media/nathaniel/Data/catkin/build/CMakeFiles/CMakeOutput.log".
See also "/media/nathaniel/Data/catkin/build/CMakeFiles/CMakeError.log".
nathaniel@nathaniel:/media/nathaniel/Data/catkin/build$ `

I am not sure how to solve this problem can anybody help me out?