This week's book giveaway is in the Testing forum. We're giving away four copies of The Way of the Web Tester: A Beginner's Guide to Automating Tests and have Jonathan Rasmusson on-line! See this thread for details.
As can be seen, HelloRemote is an interface which should be available on the client side. Have you packaged the interface class in a JAR and included in the client application?
What is your project configuration?