I'm just getting started with ZF

I'm doing fine with:
but:
gives the error:

Fatal error: Uncaught exception 'Zend_Gdata_App_InvalidArgumentException' with message 'Property __description does not exist' in /home/djtutor/library/Zend/Gdata/App/Base.php:355 Stack trace: #0 /home/djtutor/library/Zend/Gdata/App/Base.php(335): Zend_Gdata_App_Base->__isset('__description') #1 /home/djtutor/library/Zend/Gdata/YouTube/UserProfileEntry.php(296): Zend_Gdata_App_Base->__set('_description', Object(Zend_Gdata_YouTube_Extension_Description)) #2 /home/djtutor/library/Zend/Gdata/App/Base.php(200): Zend_Gdata_YouTube_UserProfileEntry->takeChildFromDOM(Object(DOMElement)) #3 /home/djtutor/library/Zend/Gdata/App/FeedEntryParent.php(120): Zend_Gdata_App_Base->transferFromDOM(Object(DOMElement)) #4 /home/djtutor/library/Zend/Gdata/App/MediaEntry.php(76): Zend_Gdata_App_FeedEntryParent->__construct('<?xml version='...') #5 /home/djtutor/library/Zend/Gdata/Entry.php(45): Zend_Gdata_App_MediaEntry->__construct('<?xml version='...') #6 /home/djtutor/library/Zend/Gdata/YouTube/UserProfileEntry.php(220): Zend_Gdata_Entry-> in /home/djtutor/library/Zend/Gdata/App/Base.php on line 355

What am I doing wrong?

Can you provide any more data? Maybe some additional code? It's difficult to determine the issue with a single line of code.