Reference other files from XFBRStringService

Hi, 

I've created an XFBR String Service file, and I would like to reference other (also XFBR String Service) files to break up the XFBR rule to manageable pieces. I keep running into compile issues. Any insights would be helpful. Thanks. 

Here are the screenshots of what I have: 

-Main XFBR String Service file (referenced in the Service Factory):

-The secondary XFBR String Service file I'm calling & error: