Image scanning using WIA - WiaClass not getting

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C#

C#4.0

Dear All,
I am developing a image scanner application in VS2010, windows 7.
I added wiaaut.dll as reference in my project.
WIA namespace included in the code.But when I am creating object of WiaClass its showing error as 'class could not be found'.
I want to create object of all these classes.

WiaClass wiaManager = null;       // WIA manager COM object
   CollectionClass wiaDevs = null;   // WIA devices collection COM object
   ItemClass wiaRoot = null;         // WIA root device COM object
   CollectionClass wiaPics = null;   // WIA collection COM object
   ItemClass wiaItem = null;         // WIA image COM object

But it is showing error. Please help me...