For anyone arriving here after installing Visual Studio 2015 Update 1 and then updating some packages, here is what fixed it for me:
- Close Visual Studio
- Delete %LocalAppData%\Microsoft\VisualStudio\14.0\ComponentModelCache
- Re-open Visual Studio
I was getting this error message in VS2015 and the fix worked for me, so it seems to apply to 2013 and 2015.
I found the solution on another Stack Overflow question: Visual Studio 2015 Broken Razor Intellisense.