“During the final testing phases for our Windows Phone Developer Tools CTP refresh, we discovered a bug that’ll impact developers using some existing “transparent Silverlight” assemblies (Microsoft & 3rd party) in Windows Phone applications, with regard to loading of signed precompiled assemblies in context of your app,” stated Brandon Watson. Detecting Problem: If your app deploys to the emulator, but fails to run with a “System.IO.FileLoadException” then you may be using a signed assembly. These’ll be assemblies you manually added to your project. For e.g., if you’ve an app that uses System.ServiceModel.Syndication.dll (assembly shipped with Silverlight SDK and thus is digital signed) and you try to run that app in emulator it’ll fail in debugger with error like: A first chance exception of type ‘System.IO.FileLoadException’ occurred in mscorlib.dll. “Workaround: Temporarily use copies of assemblies which don’t have signing certificates in them. I’ve provided a PowerShell script that make creating these copies easy. Simply run it, specifying path to assembly you want to use, and it’ll create a copy with an easily identifiable filename prefix of “WP7_CTP_Fix”. You can then use this assembly with CTP Refresh. Copy script to a folder on your machine and follow steps similar to these. PowerShell is built into Windows 7. If you’re running Windows Vista, install PowerShell,” explains Watson.