If you get a "Unable to Reference DAO Object Library" or "Method MethodName of Object ObjectName Failed" error message when trying to use DAO VBA code in Access 2016 / 365, but you've set a reference to the DAO 3.6 Object Library, or if you're trying to add a reference to the DAO 3.6 Object Library but Access won't let you; then the issue is that you're already using DAO but not with the DAO 3.6 Object Library.

Turns out that DAO is now part of "Microsoft Office 16.0 Access database engine Object Library".

So, make sure you're using the appropriate reference for your version of Access, i.e. Microsoft DAO 3.x Object Library (Access 97 - 2003) or Microsoft Office 1x.x Access database engine (Access 2007 onwards)).