A potentially dangerous Request.Form value was detected from the client

This issue happening if we entered text in controls that look like HTML statement. We can omit this issue  to set validation request is False.

<%@ Page Language="C#" MasterPageFile="~/ControlPanel/Site1.Master" ValidateRequest="false" AutoEventWireup="true" CodeFile="Cookies.aspx.cs" Inherits="ControlPanel_Cookies" %>

We can set this settings in globally when we write like below in web.config
<pages validateRequest="false" />