Recuperar objeto de una session

[Legolas_Bilbao]

me da este error
Fatal error: main() [function.main]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Medico" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in C:\Archivos de programa\Apache Group\Apache2\htdocs\php\MenuMedico.php on line 16