Please consider updating the Caliburn NuGet packages to also include the SymbolSource packages.

Here are links from NuGet documentation and from SymbolSource on how to set it all up.

Pretty straight forward and should be a quick win.

http://docs.nuget.org/docs/creating-packages/creating-and-publishing-a-symbol-package 

http://blog.davidebbo.com/2011/04/easy-way-to-publish-nuget-packages-with.html

Here's how to set Visual Studio up for source stepping from the SymbolSource servers:

http://www.symbolsource.org/Public/Home/VisualStudio

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