I see your issue:  you have a typo in the class name.  You have "HelloWordService", and it should be "HelloWorldService".  You're missing the "l".  I took your code, pasted it into my solution, fixed the typo, and it runs perfectly.  I also double-checked the doc from where you would have gotten the code, and I do not notice a typo in the original doc, so somehow that typo snuck in there and tripped you up.

Hope that helps.

--Tim