WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive).

Error in 2012 VS when using validation control :

Server Error in '/it' Application.

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WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive).

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive).

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[InvalidOperationException: WebForms UnobtrusiveValidationMode requires  a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping  named jquery(case-sensitive).] System.Web.UI.ClientScriptManager.EnsureJqueryRegistered() +2170706 System.Web.UI.WebControls.BaseValidator.RegisterUnobtrusiveScript() +10 System.Web.UI.WebControls.BaseValidator.OnPreRender(EventArgs e) +9576593 System.Web.UI.Control.PreRenderRecursiveInternal() +83 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Page.ProcessRequestMain(Boolean  includeStagesBeforeAsyncPoint,Boolean includeStagesAfterAsyncPoint) +974

Solution:
Add in web.config :

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