My RIA service was returning "not found" so I used fiddler and it show error 500. But its not return a description that tell me the problem. It just showes some gaubage on the "Webview" tab. All the nessary files domain sevice files have been copied over.
Have you looked at this blog post? http://blog.discountasp.net/how-to-troubleshoot-silverlight-ria-applications/
