I love it when I see "The Project file '' has been renamed or is no longer in the solution"! Its just not a very detailed error and doesn't even tell you what project its looking for.
What the error really means is you have a project reference and that project is no longer in the solution. This happens a lot with web projects and the easiest way to solve it is right click on your project and go to "Property Pages" and in the References section you'll see the reference name and the offending reference will have (unavailable) next to it.