Set ValidationSettings:UnobtrusiveValidationMode to None in web.config file to resolve this issue.
I got an error while adding Asp.Net validation control to my page. Error was "WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive)". I checked everywhere in my application for the error but was unable to identify that. It was troubling me a lot as implementing validtion to your page is the basic requirement and anyhow it must be implemented.
You can resolve this issue adding only one line of code in your config file. Simply add this code in your web.config file and you will be happy.
<add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
Hope this can help you.