Newbie question: FormDataEvent isn't firing

I'm an experienced .NET programmer but am new to SBO 2005. I've been working on an add-on to customize some of our forms and have figured out most of the ItemEvent events. But I need to change how items are displayed in a combobox attached to a datasource. So I'm assuming I need to capture the FormDataEvent event, but I can't seem to figure out how to get it to fire.

Keep in mind that this is right next to an ItemEvent sub that works fine.

What am I missing? Could this be some sort of licensing issue?