I always forgot how to register .Net in IIS so i will write it here
The following command installs the ASP.NET version associated with the tool and updates the script maps of all existing ASP.NET applications. Note that only applications that are currently mapped to an earlier version of ASP.NET are affected.
type this in command prompt
for full information can be seen in http://msdn.microsoft.com/en-us/library/k6h9cz8h%28v=vs.71%29.aspx