When you install the .Net framework on your web server, it installs some script files (including the above) under the root folder (usually "C:\inetput\wwwroot" if you do a default installation) .
You can then find the above file at "C:\Inetpub\wwwroot\aspnet_client\system_web\1_1_4322", for example.
The above problem could happen if you reconfigured your web root directory to be a different one after you installed ASP.Net in your web server. If that is the case, then run 'aspnet_regiis -c' (utility is under %windir%\Microsoft.NET\Framework\v1.1.4322, for example) or copy over manually the above script files into a similar sub-directory below your current web root directory. Also, if you look at the error message in detail, you will notice where the file is supposed to be.