I downloaded Deep Zoom Composer here:
And open and compiled the demo Silverlight app. in the folder "Deep Zoom Classic + Source".
It throws an exception when it run whether I upgrade the code to ASP.NET 4.0 or keep it at the level it was designed for.
I think it's because the authors expected me to create my own XAP file. I have now done this but cannot find how to add this to the solution.
I hope someone handy with Silverlight could take the 5 minutes to reproduce the problem.