openstack error

[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81] mod_wsgi (pid=23541): Exception occurred processing WSGI script '/usr/share/openstack-dashboard/openstack_dashboard/wsgi/django.wsgi'.
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81] Traceback (most recent call last):
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]   File "/usr/lib/python2.6/site-packages/django/core/handlers/wsgi.py", line 219, in __call__
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]     self.load_middleware()
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]   File "/usr/lib/python2.6/site-packages/django/core/handlers/base.py", line 37, in load_middleware
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]     for middleware_path in settings.MIDDLEWARE_CLASSES:
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]   File "/usr/lib/python2.6/site-packages/django/utils/functional.py", line 184, in inner
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]     self._setup()
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]   File "/usr/lib/python2.6/site-packages/django/conf/__init__.py", line 42, in _setup
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]     self._wrapped = Settings(settings_module)
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]   File "/usr/lib/python2.6/site-packages/django/conf/__init__.py", line 95, in __init__
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81]     raise ImportError("Could not import settings '%s' (Is it on sys.path?): %s" % (self.SETTINGS_MODULE, e))
[Fri Jul 10 16:44:03 2015] [error] [client 172.16.0.81] ImportError: Could not import settings 'openstack_dashboard.settings' (Is it on sys.path?): No module named pkg_resources