If you find this error when trying to set up your website, just open a command prompt and type:
cd c:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\ aspnet_regiis.exe -iru
And then:
cd.. cd v2.0.50727 aspnet_regiis.exe -iru
This will register again asp.net 4 & 2 and hopefully your problem will be solved.