how to rename a project without killing solution

When I rename a project within a solution, and then try and build that project, I get the error: "The project file "xyz.csproj" was not found. Where xyz is the old project file name!

The annoying thing is that I can search my project & solution for the old project file name, and the search will come up with nothing, and when I click on the error VS does nothing.

So there seems to be no way of finding where the old reference is.

This is a .web project hosting a silverlight page, if that makes any difference.