If you are using .NET Framework 3.5 Beta 2 to create WPF applications that support visual add-ins, you should be aware that, in the forthcoming .NET Framework 3.5 RTM, the naming of both the System.AddIn.Pipeline.VisualAdapters class and its members have changed from this  to this .
Consequently, you’ll need to change your code to use the new type and member names for .NET Framework 3.5/Visual Studio 2008 RTM.
 .NET Framework 3.5 Beta 2.0namespace System.AddIn.Pipeline
public static class VisualAdapters
public static INativeHandleContract ViewToContractAdapter(Visual);
public static FrameworkElement ContractToViewAdapter(INativeHandleContract);
 .NET Framework 3.5 RTMnamespace System.AddIn.Pipeline
public static class FrameworkElementAdapters
public static INativeHandleContract ViewToContractAdapter(FrameworkElement);