norton compains about that error all the time, not only with your custom apps. and it is not an important issue which would need to be fixed.
a creator code of
? is okay, it wont cause any problems. it is just a way of saying "i dont have a creator code". it is common to also type this in manually, for example using a hex editor.
works likewise with the type code ... of course applications, desktop accessories or fonts must have a proper type code for a #reason
... but for most types of documents it is technically okay.