ImportError: No module named urlresolvers when start

1. install freezer-web-ui
2. start httpd
3. visit the horizon url
4. some error in /var/log/httpd/horizon_error.log

2016-02-24 10:57:12.058152 mod_wsgi (pid=31435): Exception occurred processing WSGI script '/home/kevin/openstack/horizon/openstack_dashboard/wsgi/django.wsgi'.
2016-02-24 10:57:12.058252 Traceback (most recent call last):
2016-02-24 10:57:12.058283 File "/usr/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 170, in __call__
2016-02-24 10:57:12.058410 self.load_middleware()
2016-02-24 10:57:12.058434 File "/usr/lib/python2.7/site-packages/django/core/handlers/base.py", line 52, in load_middleware
2016-02-24 10:57:12.058553 mw_instance = mw_class()
2016-02-24 10:57:12.058565 File "/usr/lib/python2.7/site-packages/django/middleware/locale.py", line 24, in __init__
2016-02-24 10:57:12.058625 for url_pattern in get_resolver(None).url_patterns:
2016-02-24 10:57:12.058636 File "/usr/lib/python2.7/site-packages/django/core/urlresolvers.py", line 401, in url_patterns
2016-02-24 10:57:12.058848 patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
2016-02-24 10:57:12.058871 File "/usr/lib/python2.7/site-packages/django/core/urlresolvers.py", line 395, in urlconf_module
2016-02-24 10:57:12.058892 self._urlconf_module = import_module(self.urlconf_name)
2016-02-24 10:57:12.058904 File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module
2016-02-24 10:57:12.058956 __import__(name)
2016-02-24 10:57:12.058969 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../openstack_dashboard/urls.py", line 36, in <module>
2016-02-24 10:57:12.059088 url(r'', include(horizon.urls)),
2016-02-24 10:57:12.059144 File "/usr/lib/python2.7/site-packages/django/conf/urls/__init__.py", line 34, in include
2016-02-24 10:57:12.059251 patterns = getattr(urlconf_module, 'urlpatterns', urlconf_module)
2016-02-24 10:57:12.059274 File "/usr/lib/python2.7/site-packages/django/utils/functional.py", line 225, in inner
2016-02-24 10:57:12.059488 self._setup()
2016-02-24 10:57:12.059513 File "/usr/lib/python2.7/site-packages/django/utils/functional.py", line 376, in _setup
2016-02-24 10:57:12.059538 self._wrapped = self._setupfunc()
2016-02-24 10:57:12.059551 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../horizon/base.py", line 825, in url_patterns
2016-02-24 10:57:12.059881 return self._urls()[0]
2016-02-24 10:57:12.059971 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../horizon/base.py", line 860, in _urls
2016-02-24 10:57:12.060005 include(dash._decorated_urls)))
2016-02-24 10:57:12.060015 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../horizon/base.py", line 534, in _decorated_urls
2016-02-24 10:57:12.060039 include(panel._decorated_urls)))
2016-02-24 10:57:12.060055 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../horizon/base.py", line 307, in _decorated_urls
2016-02-24 10:57:12.060078 urlpatterns = self._get_default_urlpatterns()
2016-02-24 10:57:12.060087 File "/home/kevin/openstack/horizon/openstack_dashboard/wsgi/../../horizon/base.py", line 113, in _get_default_urlpatterns
2016-02-24 10:57:12.060101 urls_mod = import_module('.urls', package_string)
2016-02-24 10:57:12.060109 File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module
2016-02-24 10:57:12.060124 __import__(name)
2016-02-24 10:57:12.060132 File "/home/kevin/devstack/src/freezer-web-ui-origin-master/disaster_recovery/sessions/urls.py", line 18, in <module>
2016-02-24 10:57:12.060199 from disaster_recovery.sessions import views
2016-02-24 10:57:12.060217 File "/home/kevin/devstack/src/freezer-web-ui-origin-master/disaster_recovery/sessions/views.py", line 21, in <module>
2016-02-24 10:57:12.060293 import disaster_recovery.sessions.browsers as project_browsers
2016-02-24 10:57:12.060318 File "/home/kevin/devstack/src/freezer-web-ui-origin-master/disaster_recovery/sessions/browsers.py", line 17, in <module>
2016-02-24 10:57:12.060395 from disaster_recovery.sessions import tables
2016-02-24 10:57:12.060465 File "/home/kevin/devstack/src/freezer-web-ui-origin-master/disaster_recovery/sessions/tables.py", line 22, in <module>
2016-02-24 10:57:12.060631 from horizon.utils.urlresolvers import reverse
2016-02-24 10:57:12.060741 ImportError: No module named urlresolvers