While making a website in MVC3 on ASP.NET, I got the error: “The entry ‘xyz’ has already been added.”.
I realized that somehow my data Context was already being created by EF and I was getting this error.

The fix for this was to change my ConnectionString (in web.config) to not be of this same name.

I realized that in code-first models, the connection string had to match the database being created, which should match the context class, derived from DbContext.  This was happening in this “database-first” case as well.

I made this short post because many folks are baffled by this error, and I hope this post helps them.