the SpellCheck.aspx first line already looks like this
<%
@ Page Language="C#" ClassName="PopUpSpell" ValidateRequest="False" %>
my project web.config looks liek this
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.web>
<machineKey validationKey="A96B2F3BF50A1A2A1B81214A550B89F2A318B3712FB5AC8CD82AF4F3925B3C6ED58CF5F38503629A78BF8C27B1B736C4E84DACE342AB83A42932B44EBC3D7601" decryptionKey="D01201C69DF5E9863133028CBD4E6EEFC45B5E609D7F4107" validation="SHA1" />
<healthMonitoring enabled="true">
<rules>
<add name="All Errors Email" eventName="All Errors" provider="EmailWebEventProvider" profile="Default" minInstances="1" maxLimit="Infinite" minInterval="00:00:10" />
</rules>
</healthMonitoring>
<pages validateRequest="false" enableEventValidation="false" controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID">
</pages>
<!-- error stuff goes here-->
<customErrors defaultRedirect="Error.aspx" mode="Off">
<error statusCode="404" redirect="Error.aspx?e=404" />
</customErrors>
<!--
Set compilation debug="true" to insert debugging
symbols into the compiled page. Because this
affects performance, set this value to true only
during development.
-->
<compilation debug="false" targetFramework="4.0">
<assemblies>
<add assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
<add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
<add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Web.Extensions.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /></assemblies>
</compilation>
</system.web>
<location allowOverride="true">
<appSettings>
<add key="ProductionServer" value="PRODUCTION1" />
</appSettings>
<system.web>
<sessionState timeout="60" />
</system.web>
<system.webServer>
<httpErrors>
<remove statusCode="404" subStatusCode="-1" />
<error statusCode="404" prefixLanguageFilePath="" path="/redirects.aspx" responseMode="ExecuteURL" />
</httpErrors>
</system.webServer>
</location>
</configuration>