This release is just a minor one after almost 3 years of suspension of the project. BlogML 2.1 applies the exact same specification and XML schema as BlogML 2.0, and only fixes a bug in the .NET API library.
All you need to do is replacing BlogML.Dll file in all your project. You don't need to change anything else or even recompile your projects.
For more information about this build and the future of the project read this blog post:http://nayyeri.net/blogml-2-1-released