Delphi --- problem when using function RegisterClass

Delphi has a feature: serialize/deserialize object. It means you can save/load object at runtime.
To do this, your classes have to inherit from TPersistent and you have to register this class to system. To register a class you can you function: RegisterClass. After registering successfully, you can read or write object to the stream. But there are problems: you can not know if class is registered successfully till you call function: getclass or findclass, and you can not know why it is not succeeded. It takes me 1 day to find why it can not register. All i have to do is debug delphi system to find out the reason. And i want to share my experience when i face this problem. The reason is: the class belongs to a group. But this group is deactivated when delphi create group. So this class can not be registered. All we have to do in this case is activate group again by calling function activategroup(class belong to group). Hope i can help you to save time when solve this problem