Changing the ASP.NET version of a Web site in IIS6 using the IIS Manager GUI requires a restart of the W3SVC service. This means that all sites on your Web server will be affected and sessions will be lost. This isn’t really desirable behavior if you are hosting more than one site on a Web Server.
Although one doesn’t often need to upgrade the ASP.NET version of a Web site, it’s important to know how to do so without affecting the remaining sites on the server.
Also, when you are creating a new Web site IIS6 doesn’t allow you to select the version of ASP.NET that you want to use. This is a problem since you must first set the site up, and IIS will default behind the scenes to an ASP.NET version of its choosing (usually the lowest version of ASP.NET you have installed on the server).
In either case of creating a brand new site, or upgrading an existing site it is important to know how to change the version of ASP.NET without needing to affect all of the sites on your Web server by restarting the W3SVC service.