“The type ‘System.IO.Packaging.Package’ is defined in an assembly that is not referenced.” Error

Today , when I was working with the Open Office XML 2.0 SDK and adding the reference to the DocumentFormat.OpenXML assembly file and tried to build the project , i got the below compiler error message.

“The type ‘System.IO.Packaging.Package’ is defined in an assembly that is not referenced. You must add a reference to assembly ‘WindowsBase, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’.”

The fix was really simple. Adding the Windows Base assembly to the project solved the problem.

If you are using, Visual Studio 2012, just search for the WindowsBase in the Assemblies -> Framework in the Add Reference Dialog.