Can't run aspx with Ajax on my new win 8 pro

Hi,

I have win 8 with iis I try to test my progs locally.

An old util based on Ajax that worked fine on the iis of win xp giving now an error says it can't load file of extension, referring to the line in the web.config file:

<add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>

please tell your advice.