Please try to use Fiddler as explained in this blog post:http://blogs.esri.com/Dev/blogs/silverlightwpf/archive/2009/08/24/Troubleshooting-blank-layers.aspx
And what did you see in the Fiddler requests and responses? Is metadata requested? Are images requested? And if so do they fail? Is your service returning images if you go to the REST endpoint and try and export the map manually?
And what did you see in the Fiddler requests and responses? Is metadata requested? Are images requested?
Fiddler does not show any error, it just not returning the images.
The address of my website is http://134.121.117.16/xwu_sl_app/xwu_sl_app_web/xwu_sl_apptestpage.aspx, you can try visiting.
Keep in mind that this application runs perfectly on the computer where I developed the sl app.