I had met a peculiar Apache 2 error on Drupal upgrading. I can see my site loaded but can't access any of the sub-URL's in the site. When I provide the Url:www.test.com/admin/node, its shows "Requested URL /admin/node not found on this server". But if the url is provided like 'test.com/?q=node/', it allows to get the link.
I checked with the error log and found that the clean url are not redirecting. The problem was with the apache2.conf file change on Drupal upgrade.
While discovering the apache2.conf file, found that the limit access is changed to default in the file where virtual host is specified.
Options FollowSymLinks AllowOverride None Require all denied
So,I just needed to change AllowOverride None to AllowOverride All in the file.
Options Indexes FollowSymLinks AllowOverride All Require all granted
The problem is solved with this approach and the Drupal site updated with clean URL's.