I am just doing a simple SL app to just display a map. When I add the esri:PictureMarkerSymbol I get the following error when I build the solution:
"Could not load file or assembly 'System.Runtime.Serialization, Version=22.214.171.124, , Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or one of its dependencies. The system cannot find the file specified."
If I comment out the esri:PictureMarkerSymbol xaml I can build the solution without error.
I am using VS10, ESRI 2.0 API beta and the 3.5 .Net Framework.