Few days back I worked on an issue where an application compiled using Visual Studio 2010 C# Express edition was getting ‘null’ at “Application.ActiveProject.CustomDocumentProperties” when trying to follow below article :

How to Use Automation to Get and to Set Office Document Properties with Visual C# .NET
http://support.microsoft.com/kb/303296/en-us

Cause

The issue was found to be due to a bug in the NOPIA code generated by Visual Studio 2010 C# express edition. This issue is fixed in the latest versions of Visual Studio Express editions (VS 2012 Express Edition for C# or VS 2013 Express Edition for C#)

Work Around

Set the “Embed Interop Types” property to “False” for the MSProject PIA references added to project