This error means your host does not support Xcache. That’s why you need to switch to Memcache.
You may get this error even if you disabled cache in your store. But fix for this is very simple.

PrestaShop 1.6
Go to config/settings.inc.php and change define('_PS_CACHING_SYSTEM_', 'CacheXcache'); to define('_PS_CACHING_SYSTEM_', 'CacheMemcache');

PrestaShop 1.7
Go to app/config/parameters.php and change 'ps_caching' => to 'CacheMemcache'

Save the file and now it should be fine.