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

Solution : 

<%@ Page Title="" Language="VB" MasterPageFile="MasterPage.master" AutoEventWireup="false" CodeFile="addcourse.aspx.vb" Inherits="addcourse" ValidateRequest="false" %>

add 

ValidateRequest="false"

 web config 

add

<httpRuntime requestValidationMode="2.0" />

after 

<system.web>