In this blog post, Vincent Leung explains what causes and how to avoid the following error - "The remote server returned an error: NotFound".
Have you seen this error message before? “The remote server returned an error: NotFound.”, Not particularly helpful! This is your Silverlight app’s way of telling you that there was an exception during a WCF Service call. You can fix this with a little WCF server-side magic. The magic is described in the Silverlight documentation in an entry called Creating and Handling Faults in Silverlight.