There is issue with CMemCache cache, for example there is no checking in MemCache init function idf extension is not loaded, like it is done for other cache extensions.
So, there should be code like:
public function init()
{
parent::init();
if(!extension_loaded('memcache'))
throw new CException(Yii::t('yii','CMemCache requires PHP memcache extension to be loaded.'));
...
...
}