I think your problem is that you have all the JARs included in your project. Remove all JARs except the following:
com.noelios.restlet.jar and org.restlet.jar
Try compiling your project and, if compilation fails, add JARs as needed.
Do not add JARs you do not need - for instance, the error you get is related to the Restlet-Google Web Toolkit integration, something you do not need for the example program.