How to fix search result "Access denied You are not authorized to access this page"
In admin/people/permissions, make sure that the roles that should be allowed to search are checked. Under the Search heading, look for the Use search permission. If anonymous users need this permission, check the box next to Anonymous User.
Next, clear your Drupal cache.

If you use Drush, you can use the following command.

drush cc all


There are several other ways to clear your cache as well.

Lastly, you can try rebuilding your permissions at admin/reports/status/rebuild.