Yeah, whenever you have a component designer attached to something, you have to make its base class non-abstract.  Because the designer actually creates an instance of the base class and uses that as the root of the designer... rather than the class itself (I have no idea why, but I'm sure they've got a good reason for doing so).  So, when we have a base class for our business objects, we generally create a property/method that needs to be overriden and throw a NotImplementedException() from within the base class (rather than making it abstract/MustInherit, because you can't), so that way, when you forget to override it in one of your classes, you'll get a nice red error window telling you what method you forgot to override.  (just don't forget to NOT call the MyBase.Method() or it will still throw the exception ).