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

by default asp.net checks for the scripts in requests so that if it finds a user that is posting javascript or HTML in a request body it will throw an exception "A potentially dangerous Request.Form value was detected from the client"

but sometimes you need this like when you allow a user to send HTML formatted block like in an article or if you are building a blog engine and u need to enable the user to add affiliation site codes or a google analytics block

in this case all you have to do is to modify your page directive to be

   1: <%@ Page Language="c#" AutoEventWireup="false" ValidateRequest="false" %>

ValidateRequest attribute makes sure that asp.net disables this validation

you can also add this node to the page section in web.config

   1: <pages validateRequest="false" />

but of course this is not recommended as it would disable all validation on all pages.

when using these changes please do not forget to make your own validation