Hi,
I'm developing a silverlight application that consumes a webservice. Calls to this webservice are made Asynchronously. But when an exception occurs during a procedure of the async call, I get an error on the completed event but i lost my original exceptions information. Independent of what the original exception was, I always get "The remote server returned an error: NotFound" back, with stack that points to "external" code.
Any advice?
This happens with any exception in your SL to WCF, sometimes you can find the innerexception with Fiddler2 in the transfered data or you might see the HTTP error code which can give you a hint , other times it's harder to find. This is my big request item for SL 4.0, better WCF debugging.
When the service throws an exception it's translated to a 40(x) HTTP response that gets handled by the browser before the Silverlight plugin can handle it. To avoid this, wrap your WCF calls in a try/catch block and send exception data back to the client through an HTTP response that can be handled by Silverlight, such as 200. Here's a terrific implementation of this strategy on codeproject: http://www.codeproject.com/KB/silverlight/SilverlightExceptions.aspx
Follow James Cadd's advice above. Getting more informative error messages will certainly help and, unfortunately, you can't rely on the debugger to generate them for you.
Even if you're not a big fan of unit testing, this is a place where it's more than worthwhile. Constructing a set of tests that will purposefully send your webservice bad data and making sure that you get back informative errors will help set you up to figure out why it's not working with the Silverlight app. Writing these kinds of tests takes a different way of thinking, but it will give you a lot of confidence in your code if you know that you've tried to break the webservice in every possible way and it always gives you back something you can use to trace the problem.