PHP错误 急，在线等！！

The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Car" 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 D:\TsbGameWebSystem\back_car.php on line 15

程序尝试去解释一个对像的方法或属性，请确认你要操作的类里在调用"loaded_before_unserialize()"之前已定义”Car”，或提供一个__autoload()的方法加载类的定义，在D:\TsbGameWebSystem\back_car.php 的行15

意思就是说你调用Car这个属性或方法之前没有对他进行定义！