Class 'CToolsCssCache' not found

I couldn't figure out why it happens actually but I had this error in every access to the website:

 PHP Fatal error:  Class 'CToolsCssCache' not found in /var/www/web/includes/cache.inc on line 31

The only CTools activated module I 've got is this: Chaos tools7.x-1.6

This class is loaded becasuse there is a variable set like this:

cache_class_cache_ctools_css: "CToolsCssCache"

And _cache_get_object function in cache.inc is trying to load it. May be the database is "corrupted" from previous configuration but I didn't want to delete that variable.

My current solution is to edit the settings.php file by adding this piece of code:

/**
 * Pre include(?) CToolsCssCache
 */
// $conf['cache_class_cache_ctools_css'] = 'CToolsCssCache'; //<-- doesn't work

require_once __DIR__ . '/../../includes/cache.inc';
require_once 'sites/all/modules/ctools/includes/css-cache.inc';

I left a comment saying that I used a possible solution found in other forums didn't work. They don't talk about this class, but I tried anyway.

I'm not quite happy with this solution as I don't know the origin of this issue. But at least I hope it could help someone or someone could explain what is going on.

Regards.