When calling a class like Zend_XmlRpc_Value_Array before any other Zend_XmlRpc subclass (eg : Zend_XmlRpc_Client, Zend_XmlRpc), php gives fatal error : "Class 'Zend_XmlRpc_Value_Collection' not found" The problem resides in the require_once order : first is called Zend_XmlRpc_Value_Array which require_once Zend_XmlRpc_Value_Collection which require_once Zend_XmlRpc_Value which require_once Zend_XmlRpc_Value_Struct which require_once Zend_XmlRpc_Value_Collection -- well, it's already required so skip this one then Zend_XmlRpc_Value_Struct tries to extends Zend_XmlRpc_Value_Collection but the file still is not loaded, because we are deep down the including process. So the Class Zend_XmlRpc_Value_Collection cannot be found.

Possible fix would be to require mother class Zend_XmlRpc_Value before anyone else.