Objects inside Sessions

Hi, I'm having a little problem when I put an object inside a session variable. I have the following code which brings me an object if it is set in _SESSION or creates a new one if it is not set. It is working almost fine except that sometimes it gives me the freak message "Fatal error: Unknown(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition library of the object you are trying to operate on was loaded _before_ the session was started in /xxx/.../.../.../file.php on line 12". The code: <snip> function coreNewObject($class, $arg = '') { if(!isset($_SESSION['CORE_OBJECTS'])) $_SESSION['CORE_OBJECTS'] = array(); if(isset($_SESSION['CORE_OBJECTS'][$class])) { $init = "{$class}Init"; if(method_exists($_SESSION['CORE_OBJECTS'][$class], $init)) $_SESSION['CORE_OBJECTS'][$class]->$init($arg); return($_SESSION['CORE_OBJECTS'][$class]); } if(class_exists($class)) { $_SESSION['CORE_OBJECTS'][$class] = new $class($arg); return($_SESSION['CORE_OBJECTS'][$class]); } return(false); </snip> This happens in a page that contains... <snip> /* library class definition */ require_once("includes/library.class.php"); /* this initializes the session and do some other stuff */ Core::Core(); if($_REQUEST['clear']) session_destroy(); $lib = Core::coreNewObject('Library'); /* the error occurs here! */ $lib->libSetCategoryReference(); </snip> I find this behavior strange 'cos this only happens when I do a 'reload' on the page. Normal navigation, through links and so, doesn't gives me any errors. Also, session.auto_start is not set. What are the reasons why an object gets a "__PHP_Incomplete_Class" status? Any suggestions? You may contact me in PVT if you want.. I tried some archives digging but didn't find any lights... Thanks, William