WPF Designer issue for UserControl

Question

hi, 

i'm a windows forms guy and i'm starting my first WPF app and had an issue. my goal here is to create basically a user control inside a Window class but i'm having trouble at design time. 

i tested with Mahesh Chand's wpf usercontrol example and everything worked perfectly in vs 2008. (thanks Mahesh) but for some reason the designer is not working for me in vs 2010.

http://www.c-sharpcorner.com/uploadfile/mahesh/wpfusercontrol06292008215701pm/wpfusercontrol.aspx?login=true&user=amaiz09

i made sure my namespace declarations were added but had no intellisense and getting getting an error that the compiler was "Unable to load the metadata for assembly..." 

the application works fine at runtime. 

your help is greatly appreciated!!

Thanks

Al