Compiler error: Same identity, EnvDTE80

Trying to follow this tutorial, under the section "Initializing the Project Factory" I've added EnvDTE to my project, but 开发者_StackOverflow中文版now I get this error:

An assembly with the same identity 'EnvDTE80, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' has already been imported. Try removing one of the duplicate references.

Even if I remove all the references to it, I still get it. It must be somewhere in the project base or something? What's creating two+ references to it?

Resolved this particular error by unloading the project, editing the .csproj xml file and removing the reference to EnvDTE in there.