RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
If not, then change the code of the .htaccess file according to the above rule.
If you don't have a .htaccess file, then create a new .htaccess file that contains all of the above rules.
That's it, now your problem will be fixed.