Since Microsoft is continuously upgrading the .Net framework version so you may face version conflict when deploying the Asp.Net application on IIS 6.0. When deploying two Asp.Net applications on web server one with .Net Framework 2.0 and the other with .Net Framework 4.0 your applications starts conflicting with each and may shows “Service Unavailable” when you browse your application and in the event viewer you will see some error for your ASP.Net process whose screen shot is as under: