Reproduce:WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for ‘jquery’. Please add a ScriptResourceMapping named jquery(case-sensitive)

This problem occurs while using control RangeValidation. And the answer I can use is following.

In webconfig and search for:

Delete <add key="ValidationSettings:UnobtrusiveValidationMode" value="WebForms" />

If there are no words above, adding <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" /> in ‘appSettings

At last, fresh your page.