clases en sesiones

Hello list, i have a problem with sessions and class. I used to work with a server with session.auto_start=Off, and now I had to move all my sites to another server with session.auto_start=On, and I have this problem with the session: Fatal error: Unknown(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition carrito of the object you are trying to operate on was loaded _before_ the session was started in <archive> on line 43 The problem is the class is charged after the beginning of the session, but I don't know what to do to make it work, please help me. P.D.: To put the session.auto_start in Off is not a solution because the servers administrators don't admit that. I hope you will understand my problem, sorry for my english. Thank you very much, Carlos.