Objects in Arrays

I am using PHP version 4.3.4. I'm creating an authorization module that uses a users object, that includes the username, usertype, etc. I want to store this in a session variable (i.e. $_SESSION['objects']['auth'] = new Authorization();) so that I can keep the information from page to page. However, I get an error that it is an incomplete class everytime I try to access a function from the object like this: "$_SESSION['objects']['auth']->Login();". It works fine when it's not stored in the array. Is this a PHP 4 issue? Or is there something I'm doing wrong? Any pointers would be helpful. If this doesn't work, I'll have to rework things to just store in arrays. Stuart