I've had to deal with this before. My solution was to copy the necessary files to a libs
folder adjacent to my src
directory, and reference that copied file instead. During compilation, it should get copied into the build folder along with your project's build results, and FxCop should have no issue picking it up.
I think the issue is that assemblies in the GAC don't get copied to your project's build folder, and FxCop doesn't know how to handle non-framework GAC references.
Grant Palin
2010-02-13 18:32:36