You are probably wondering why, after upgrading your Windows web server to 2008, that some of your websites are having difficulty rendering pages or are generating ASP.net errors. What someone blatantly forgot to tell you was that the ASPNET machine account has been removed from Windows Server 2008. By making this change, ASP.net now runs in a more robust and secure environment where the authentication and authorization processes can prevent certain content types. This change therefore diminished the need for a windows ASPNET account.

So what options are available to get your websites back online? There are two possible solutions you can use:

1. Install ASP.net version 1.1 on your Windows Server 2008:
   http://blogs.iis.net/bills/archive/2008/06/02/installing-asp-net-1-1-with-iis7-on-vista-and-windows-2008.aspx
2. Create a normal user account and provide the proper permissions to impersonate an ASPNET account:
   http://support.microsoft.com/?id=306158