Hi Michael,
To start, can you uninstall and reinstall the Extensibility SDK? Also, the ArcGIS API for Silverlight is included when you install the Extensibility SDK, so you don't need to install that separately.
Katy
Hi Michael,
Go ahead and uninstall both the ArcGIS Extensibility 2.2 and ArcGIS Extensibility SDK for Silverlight 2.4. Use Add/Remove programs for this. Then reinstall the ArcGIS Extensibility SDK for Silverlight 2.4.
Let me know how that goes.
Katy