EF4 Selftracking Entity

I'm wokring on building dataAcess layer for my application I'm using EF4 Self tracking entities I build entities quit well now I have to seprate self entities to their files so I can use for N tiers. So far I did follow this url http://www.codeproject.com/Articles/133689/How-to-Separate-Self-Tracking-Entities-to-Their-Ow.aspx?display=Mobile

but when I build solution it gave me error Error 2 The type or namespace name '开发者_JAVA技巧IObjectWithChangeTracker' could not be found (are you missing a using directive or an assembly reference?) C:\test\EF4 STE\STE\STEEntities\tbl_Departments.cs 22 49 STEEntities and more like this any one can help thanks