Not able to add the reference to Microsoft.XLANGs.BaseTypes.dll

This explain how to add the reference to the Microsoft.XLANGs.BaseTypes.dll in Visual Studio while working with BizTalk Projects

Microsoft.XLANGs.BaseTypes.dll is not a .Net dll and is available in the following location
<Installation Drive>:\Program Files\Microsoft BizTalk Server 2009
and you need to select Browse tab in Add Reference wizard while adding reference from the Visual Studio.