After installing a recent Windows Update, I was no longer able to run ASP.NET web apps using localhost. It seems the update removed an entry from my hosts file, located in C:\Windows\System32\drivers\etc, removing the entry that maps localhost to the loop-back IP address. The result was that pressing F5 or Ctrl-F5 to run an ASP.NET web app from Visual Studio 2008 resulted in a page in IE7 that said “Internet explorer cannot display the web page”. Interestingly, Firefox had no problem displaying the web page. To rectify the issue, I just had to open the hosts file and add the following entry:

127.0.0.1 localhost

After that IE7 displayed the web page property for localhost addresses.