Error-‘unable to find script library '/aspnet_client/system_web/1_1_4322/WebUIValidation.js’

‘unable to find script library '/aspnet_client/system_web/1_1_4322/WebUIValidation.js’ Try placing the file manually, or reinstall by running 'aspnet_regiis -c'

This error mostly occur if you are using validation controls in your website.The aspnet_client folder contains the WebUIValidation.js which is required to handle the validation controls.

To resolve this, you may need to run the following from command prompt  

%windir%\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis -c 

This will install the aspnet_client folder to the default virtual directory website. 

if you are still having this issue try following: 

a) Another potential cause of this error is that your default website is set to .NET Framework 2.0, and you're trying to debug a .NET Framework 1.1 application. In this case, you can change the setting on the ASP.NET tab of the Default Web Site's properties 

b)Check if the script files directory(/aspnet_client/system_web/1_1_4322/) in IIS manager to see whether it has been granted read access / check the folder permissions