Have recently upgraded to Visual Studio 2013 Pro and am having some teething problems.
Primarily if I change any HTML or CSS in either a .aspx page for Web Forms or
I had a similar issue and found the solution by checking the path of the virtualDirectory for your sites that are found within your applicationhost.config file.
Typically located here: C:\Users{your user name}\Documents\IISExpress\config
You want to make sure the physical path for both locations are the same since sometimes they get wonky when working on various branches/projects etc.