Hi Dale,
My best guess would be either something malformed or incorrect in the config files or a file permission problem where it can't read the files or an error in the custom one that is preventing it from building the provider collection ie when it tries to load the custom one if it has any mistakes or throws any errors it would interupt the process of building the handler collection. I would look for any clues in the mojoportal log.
Hope that helps,
Joe