After upgrading to Internet Explorer 11 (included in the recent Windows 8.1 update) my local IIS hosted web applications suddenly died. But only in Internet Explorer – the other browsers (Safari, Chrome and Firefox) were unaffected.
After some research I found out that IE 11 comes with a brand new technology called AppContainer. It’s a protection mechanism that blocks Read and Write access to most of your system, including your IIS hosted sites.
There are several ways of getting around this, but I simply turned off “Enhanced Protection Mode” under IE 11 Internet Options. I use Chrome for my daily browsing anyway, and IE is just for verifying browser compatibility of my applications. Remember to restart your browser afterwards.