Error Using Office

I add reference office.dll and Microsoft Office Excel Component to my project and use :
---------------------------------------
Dim App As Excel.Application, BarName as String

...

Dim Bar As Microsoft.Office.Core.CommandBar = App.CommandBars(BarName)

...
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Than recieve this error in my task board for the second code line:
+ 'Reference required to assembly 'Interop.Microsoft.Office.Core' containing the type 'Microsoft.Office.Core.CommandBars'. Add one to your project.'

What can I do in order to solve this problem?