We've updated our server to PHP 5.5 and S&R stopped working
Doing a quick scan through the logs, I see entries like this:
HP message: PHP Warning: mysql_real_escape_string(): A link to the server could not be established in /home/www/X/htdocs/wp-content/plugins/search-and-replace/search-and-replace.php on line 514, referer: http://X.com/wp-admin/tools.php?page=search-and-replace/search-and-replace.php
Looking through the code, it seems the now deprecated MySQL extension is being used by mysql_fetch_assoc() and others.
This extension is deprecated as of PHP 5.5.0, and will be removed in the future. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include: