// In my TaskProvider
String moduleRelativeURL = GWT.getModuleBaseURL() + "task";
target.setServiceEntryPoint(moduleRelativeURL);

// In my Application.gwt.xml:
<module>
	<inherits name='com.google.gwt.user.User'/>
	<entry-point class='com.cowgar.ontop.client.Application'/>
  	<servlet path='/task' class='com.cowgar.ontop.server.TaskServiceImpl'/>
</module>