Keep in mind that it has been a year or two since I've really played with creating and configuring websites via IIS. This is something I've done before but for some reason didn't recognize the error. I created a new website the other day and got a Configuration Error page that indicated that there was a problem with my setup that was not allowing the System.Web.Extensions namespace to load. A quick Google search revealed that I just needed to point the website's ASP.NET version should be 2.0.50727 instead of 1.1.4322.
Found the reminder here: