The FeedsSimplePieEnclosure saves a Simplepie_Enclosure in variable $simplepie_enclosure. When the FeedsSimplePieEnclosure object is unserialized the simplepie.inc has generally not been loaded so the object is incomplete.
PHP Fatal error: FeedsSimplePieEnclosure::getValue(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "SimplePie_Enclosure" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /....../modules/contrib/feeds/plugins/FeedsSimplePieParser.inc on line 21
To make the class definition be loaded before the unserialize I've added a __sleep __wakeup that does the serialization of that variable separately. [git diff a/ b/ patch so patch -p1 <]