What version are you running?
3.0.3
What's the URL of the page containing the problem?
http://localhost/admin/settings/search/?saved=1
What steps will reproduce the problem?

Go to admin settings
Go to search settings
Switch "search backend" from "Whoosh" to "Elasticsearch"
Press "Save"


What is the expected output? What do you see instead?
A nice error message or success but no error 500
What operating system are you using? What browser?
Linux, Firefox
Please provide any additional information below.
File "/var/www/dist/lib/python2.7/site-packages/django/core/handlers/base.py", line 112, in get_response

    response = wrapped_callback(request, callback_args, callback_kwargs)

  File "/var/www/dist/lib/python2.7/site-packages/reviewboard/admin/decorators.py", line 50, in decorated

    return view(request, *args, kwargs)

  File "/var/www/dist/lib/python2.7/site-packages/reviewboard/admin/views.py", line 137, in site_settings

    'root_path': settings.SITE_ROOT + "admin/db/"

  File "/var/www/dist/lib/python2.7/site-packages/django/utils/decorators.py", line 99, in _wrapped_view

    response = view_func(request, args, kwargs)

  File "/var/www/dist/lib/python2.7/site-packages/django/contrib/admin/views/decorators.py", line 17, in _checklogin

    return view_func(request, *args, kwargs)

  File "/var/www/dist/lib/python2.7/site-packages/djblets/siteconfig/views.py", line 51, in site_settings

    if form.is_valid():

  File "/var/www/dist/lib/python2.7/site-packages/django/forms/forms.py", line 129, in is_valid

    return self.is_bound and not bool(self.errors)

  File "/var/www/dist/lib/python2.7/site-packages/django/forms/forms.py", line 121, in errors

    self.full_clean()

  File "/var/www/dist/lib/python2.7/site-packages/django/forms/forms.py", line 274, in full_clean

    self._clean_form()

  File "/var/www/dist/lib/python2.7/site-packages/django/forms/forms.py", line 300, in _clean_form

    self.cleaned_data = self.clean()

  File "/var/www/dist/lib/python2.7/site-packages/reviewboard/admin/forms.py", line 1348, in clean

    search_backend_id = self.cleaned_data['search_backend_id']

KeyError: u'search_backend_id'