First of all, please make sure that you specified URL correctly.
If URL is correct, check if ASP.NET is installed and enabled in IIS. If you are using IIS7+ see below the info on for how to map .NET to IIS.
For IIS7+ the following info will ensure .NET maps to IIS:
You will need to enable the ASP.NET Feature (not using aspnet_regiis.exe) in IIS to be able to run your ASP.Net application on it, and this is how you do it:
Open Control Panel
Programs\Turn Windows Features on or off
Internet Information Services
World Wide Web Services
Application development Features
ASP.NET <-- check mark here