[ASP.NET] the type 'asystem.io.packaging.package' is defined in an assembly that is not referenced

출처: http://imak47.wordpress.com/2011/06/01/the-type-system-io-packaging-package-is-defined-in-an-assembly-that-is-not-referenced-you-must-add-a-reference-to-assembly-windowsbase/

OpenXMLSDKv2 을 설치한 후 샘플 예제를 했는데, 아래와 같은 에러가 발생하였다.

http://code.msdn.microsoft.com/office/CSOpenXmlExportImportExcel-cb196388

The type ‘System.IO.Packaging.Package’ is defined in an assembly that is not referenced. You must add a reference to assembly ‘WindowsBase’

인터넷을 검색하니 "WindowsBase"을 추가하면 된다고 한다.

Add Reference - .NET - WindowsBase