Error : WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping

Um. There really isn;t much we can suggest except "read the error message".
It tells you what you need to do in order to use "UnobtrusiveValidationMode".

So either check your naming, or look at the code you added related to unobtrusive validation mode and compare with the documentation.

We can't do any of that for you - we can't see your screen, access your HDD, or read your mind...

This error occurred on framework 4.5, here ASP.NET uses HTML5 data-attributes and late bound JavaScript from an added script reference for client-side validation logic, so to avoid this error you need to set 'UnobtrusiveValidationMode' to 'none' in web.config, add below tag in web.config to resolve it

<appSettings>
      <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
 </appSettings>