Public member 'get_Range' on type 'Worksheet' not found

I am trying to use the code in below link. It is throwing the above exception at
Dim aRange As Range = ws.get_Range("C1", "C7") http://msdn.microsoft.com/en-us/library/ms173186(v=vs.80).aspx
Excel sheet is opening.
I tried two different versions of DLL when referencing V12 and V14. Both throws the same error. How to resolve this error?
Thanks