I just installed VS2010 RC and launched the FullDuplex sample from NServiceBus 2.0.0.1145 and it ran fine. I then changed the target framework of each project in the solution to ".NET Framework 4", recompiled and launched in the debugger and received the following exception:

System.InvalidOperationException was unhandled Message=No endpoint configuration found in scanned assemblies. This usually happens when NServiceBus fails to load your assembly contaning IConfigureThisEndpoint. Try specifying the type explicitly in the NServiceBus.Host.exe.config using the appsetting key: EndpointConfigurationTypeScanned path: C:\Development\Personal\ThirdParty\NServiceBus\samples\FullDuplex\MyClient\bin\Debug\ Source=NServiceBus.Host StackTrace: at NServiceBus.Host.Program.ValidateEndpoints(IEnumerable`1 endpointConfigurationTypes) in d:\BuildAgent-02\work\672d81652eaca4e1\src\host\NServiceBus.Host\Program.cs:line 189 at NServiceBus.Host.Program.GetEndpointConfigurationType() in d:\BuildAgent-02\work\672d81652eaca4e1\src\host\NServiceBus.Host\Program.cs:line 171 at NServiceBus.Host.Program.Main(String[] args) in d:\BuildAgent-02\work\672d81652eaca4e1\src\host\NServiceBus.Host\Program.cs:line 32 InnerException: