Dear customer,

For html post on aspx page,

you should add the following code

1.  add  ValidateRequest="false" to <%@ Page %>, like <%@ Page Title="Contact" Language="C#" MasterPageFile="~/Site.Master" ValidateRequest="false" AutoEventWireup="true" %>

2. if you use asp.net 4.0,  need to add the following snippets to system.web section of web.config

<httpRuntime requestValidationMode="2.0" /> 

Regards,

Jeff