I think there is a post on that subject in this thread. If you add new categories you can no longer create nor load characters for the professions provided.
Internally each profession has costs and other important information related to the skill categories. So when you add a new category, those old professions can't cope with the change.
If you intend to play a Pulp game, you would need to remove the existing profession files and only place your own profession files.
There is a possibility, in the future, to add in ERA something to improve this situation, so that you can only add a small file to explain how to adapt existing professions to your new categories.
If you are interested in that feature, you should vote for "Extended Professions" url=http://www.ironcrown.com/ICEforums/index.php?topic=16952.0]in the poll[/url].
Also, if there is enough interest, you could ask for the specific book you are using to be added as a Package in ERA,
in this poll.
In any case, I am happy to help in this thread with any detail that you might need to make your custom pulp professions work in ERA.