In order to get the FeatureDataGrid example to work on my client I had to add in the Following name space to the top of the xaml:
xmlns:esriToolkitPrimitives="clr-namespace:ESRI.ArcGIS.Client.Toolkit.Primitives;assembly=ESRI.ArcGIS.Client.Toolkit">
After building it worked.
I took it out and re built and still worked.
Anyone know why that example would not work straight out?
Keith