When working with Silverlight, if you get an application code error 2103 and go looking for answers, you’ll find posts like this that suggest it’s a namespace problem. If that’s not the problem, you’ll find yourself stuck without many other suggestions.
Here’s a simple check for another common problem, permissions to download the Silverlight xap. Type into your browser http://localhost:8080/ClientBin/MySLControl.xap (based on your dev server and Silverlight control name) and see if you can save the file. FYI – It will show up as a zip.
If this is an asp.net site and you do have permissions issues, just add the following to your web.config:
<location path="ClientBin"> <system.web> <authorization> <allow users="?"/> </authorization> </system.web> </location>