Why can't I access IsolStorage in the System.IO namespace?

I am running VisualStudio 2012 RC on Windows 8 Release Preview.

I signed up for Win8 using my 'live' aka 'outlook' ID.

I created a new Metro Metro project. When I try to use System.IO.IsolatedStorage, Visual Studio tells me that I am missing a link. But when I go to links, add and not add, and all links are added by default.

Now, as far as I can see, IsolStorage is part of mscorlib.dll, so its "missing" is unlikely.

What am I missing?

Thanks and Regards, Sumit.