Single sign on: not able to run demo app given on google site

I am not able to run demo app as given on http://code.google.com/googleapps/marketplace/tutorial_php.html

It throws following开发者_如何学运维 error:

Fatal error: Call to a member function addExtension() on a non-object in C:\test\htdocs\index.php on line 46

I want to integrate my application using 2-Legged Oauth on a google app account.

Am I missing something?

I am working behind a proxy server. Fixing proxy in library solved this issue.