I had the same issue with an old app in iis and when running from visual studio. Disabling browser link in visual studio 2013 seems to fix this. This feature injects some javascript into your page and causes this problem for me at least. Since I disabled it now it works in IIS and from Visual studio.
VS2013 ASP.Net application error “VirtualPath was outside the current application root”
Some more details on the feature here
http://blogs.msdn.com/b/webdev/archive/2013/06/28/browser-link-feature-in-visual-studio-preview-2013.aspx
Cheers,
Crocked