I am using cakePHP 2.x . Currently doing about the twitter OAuth, http://code.42dh.com/oauth/.
function twitter_authentication()
{
//assume above
"PHP Incomplete Class" means PHP doesn't have a class definition for the object you're loading.
Option A: figure out what class that object is when you write it into the session and ensure that class's definition is loaded before loading the object.
Option B: convert the object to an stdClass or array before writing it, and convert back after loading. This might be more complex than the first option.