>Add a WCF error handler behaviour which changes the http return code to 200 even if there is an error (on the server side).
I've seen a few samples where people do this trick. However, I would rather have a naked wrestling match with a rabid grizzly bear than write some WCF behaviour code. I will bear (no pun intended) this technique in mind for the future, but for now the real fix is to use streaming. Cheers, Greg The browser sees the http 500 return code which WCF returns when an exception is thrown, which the browser gets before Silverlight, then all Silverlight sees is a http 404. See http://msdn.microsoft.com/en-us/library/ee844556(v=vs.95).aspx for more info on how to actually implement it. Although I have implemented using http://msdn.microsoft.com/en-us/library/system.servicemodel.dispatcher.ierro rhandler.aspx as I change specific exceptions into particular fault contracts globally (DomainException becomes DomainFault etc).