If you are building or maintaining COM add-ins that are based on Visual Basic 6 then this change to Office 2013 will most likely affect your add-in deployment

The Add-In Designer Object Library (msaddndr.dll) is no longer shipped with Office 2013.

Read this article for details

http://blogs.msdn.com/b/vsod/archive/2012/11/21/vb6-based-add-ins-may-fail-to-work-on-office-2013.aspx