I am getting cmake error

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Straight dump of the error message:

Traceback (most recent call last):
  File "/home/ubuntu/helloworld_ws/build/catkin_generated/generate_cached_setup.py", line 22, in <module>
    code = generate_environment_script('/home/ubuntu/helloworld_ws/devel/env.sh')
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/catkin/environment_cache.py", line 62, in generate_environment_script
    env_after = ast.literal_eval(output.decode('utf8'))
  File "/usr/lib/python2.7/ast.py", line 49, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/usr/lib/python2.7/ast.py", line 37, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    ROS_DISTRO was set to 'Ardent' before. Please make sure that the environment does not mix paths from different distributions.
                 ^
SyntaxError: invalid syntax
CMake Error at /opt/ros/kinetic/share/catkin/cmake/safe_execute_process.cmake:11 (message):
  execute_process(/usr/bin/python
  "/home/ubuntu/helloworld_ws/build/catkin_generated/generate_cached_setup.py")
Call Stack (most recent call first):
  /opt/ros/kinetic/share/catkin/cmake/all.cmake:198 (safe_execute_process)
  /opt/ros/kinetic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:52 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/ubuntu/helloworld_ws/build/CMakeFiles/CMakeOutput.log".
See also "/home/ubuntu/helloworld_ws/build/CMakeFiles/CMakeError.log".