It "repaired" and didn't change any of my project files which is a good thing.
So now I am left with a few possibilities. I think since it isn't in the global cache then that is the problem as that list looks much like what you get when you press the reference add button.
On the internet search I ran into talk of gacutil.exe with \i to add a dll file.
You have one 7.63 MB in size?