Grails & Hessian

There are so less information i could found from the internet, one official doc:

http://grails.org/Remoting+Plugin

after doing this, and i try to open the hessian service directly by browser
exception happens:
Error 500: org.springframework.web.context.request.ServletRequestAttributes cannot be cast to org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest
Servlet: hessian
URI: /GreetingCard/hessian/
Exception Message: org.springframework.web.context.request.ServletRequestAttributes cannot be cast to org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest
Caused by: org.springframework.web.context.request.ServletRequestAttributes cannot be cast to org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest
Class: Unknown
At Line: [-1]
Code Snippet:

god..