XF 1.2 XCache error when defining a backend cache ! Help

I am on a dedicated server with debian wheezy and apache.
I have installed xcache with this line command:
apt-get install php5-xcache
I have not done any custom settings for xcache.
When I put on the config.php file this line:
$config['cache']['backend'] = 'xcache';

I recieve this error with white screen on all forum pages:

An exception occurred: xcache_get(): XCache var cache was not initialized properly. Check php log for actual reason in /var/www/clients/client1/web1/web/community/library/Zend/Cache/Backend/Xcache.php on line 95

  1. XenForo_Application::handlePhpError()
  2. xcache_get() in Zend/Cache/Backend/Xcache.php at line 95
  3. Zend_Cache_Backend_Xcache->load() in Zend/Cache/Core.php at line 303
  4. Zend_Cache_Core->load() in XenForo/Model/DataRegistry.php at line 87
  5. XenForo_Model_DataRegistry->getMulti() in XenForo/Dependencies/Abstract.php at line 144
  6. XenForo_Dependencies_Abstract->preLoadData() in XenForo/FrontController.php at line 127
  7. XenForo_FrontController->run() in /var/www/clients/client1/web1/web/community/index.php at line 13
I have checked: /var/log/apache2/error.log and /var/log/messages, found nothing related to this error.
By default Xcache is allocated zero memory so my guess is that you should have a look at your php.ini file and see if thats the case and change it to whatever suits your server environment.
Also which php handler are you using?
Thank you for your reply. I am using Apache 2.0 handler.
I have looked at xcache configuration file (/etc/php5/mods-available/xcache.ini) and found that: xcache.var_size is set to 0. I changed this value to 16M and it works! (y)