How to Tell What Version of Ajax Is in a Web Configuration
- 1). Open the "Start" menu. Click on "Run." In Windows 7 and Vista, click in the search box at the bottom of the "Start" menu.
- 2). Type "%WINDIR%" into the box, without the quotes. Hit "Enter."
- 3). Double-click on the "assembly" folder and scroll down to the "System.Web.Extensions" or "System.Web.Extensions.Design" file (it doesn't matter which). In the "Version" column to the right of the file name, you will see the version number for Ajax (such as 3.5.0.0).
Source...