Getting Objects out of the $SESSION variable unscathed

I'm having a problem getting my objects out of the $SESSION variable. I am storing an ordinal array of associate arrays where one of the associate array elements is an object. Unfortunately, when I pull it back out, the object is "broken" with "__PHP_Incomplete_Class" errors. From what I can read this has something to do with 'serialization' - i.e., the emerging object must be unserialized (http://php.net/manual/en/function.unserialize.php). However, I can't get it to work. Any tips on how that is done, or what I should do instead? This program is being developed on a testing server that can then be put on a production server. Here are my server specs: Apache Version : 2.2.17 PHP Version : 5.3.3 MySQL Version : 5.5.8 Thanks in advance, Jonathan