Reviewing the details that you provided us I suppose that you are using the free version of Visual Studio 2012 where the add-ins are not supported and you could take advantage only of our Fluent Mapping API (the code only one).
If my assumption is not correct, could you please specify the version of your Visual Studio (e.g. Visual Studio 2012 Ultimate Version 11.. Upgrade 3) and does the OpenAccess ORM installer detects it in the installation process?
You could also take a look at this forum thread where the same problem is discussed for Visual Studio 2010.
I am looking forward to your feedback.
OpenAccess ORM Q2 2013 brings you a more powerful code generation and a unique Bulk Operations support with LINQ syntax. Check out the list of new functionality and improvements shipped with this release.