USBH_Device class not in GHIElectronics.NETMF.USBHost namespace

I am trying to connect a USB mouse to the ChipworkX development board and have used the code example from section 22.1 in the Beginners Guide to C# rev1.04. The problem is that the USBH_Device class is not recognised. I am using the 4.1.8.0 SDK. This prevents the delegate being recognised for the DeviceConnectedEvent. I have added the NETMF.USBHost library into the project and can see USBH_Mouse. Do I need to add another reference to the project?

You are missing GHIElectronics.NETMF.System.dll

http://www.tinyclr.com/forum/1/3056/

Thankyou. That worked.