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.
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)