Isn't it great when the answers are out there? I finally got a Google hint and overcame this one. So here are a few reasons that I encountered and overcame this error. We can easily reproduce (and often fix) this error. This occurs on the asynchronous return from a Silverlight 4 to RIA services. It's as if for any of the few reasons it fails, the call just gets aborted and we get a head-scratching "Not Found". We can sometimes even hit a debugger breakpoint in the Domain Service that gets the IQueryable call and wonder why the server appears to work in the debugger.
I’ve been looking at the Silverlight Out-Of-Browser support and the easy update feature. In the current version, we’re given the method, CheckAndDownloadUpdateAsync(). This method does a lot for us but is rather limited. With an asynchronous method and no parameters, what can we expect? With a huge team in Redmond working for us and trying to meet deadlines, we get what we get. In the spirit of sharing, here’s what I see so far.