'Sys' is undefined error on SharePoint 2007 (and ASP.NET)

When using the ScriptHandler module you may receive the 'Sys' is not defined JavaScript error. This is due to missing configurations in web.config in your SharePoint virtual folder.

Put the below settings into web.config and do an iisreset (note you may have to change the version and PublicKeyTokens to the assemblies, you have installed)

<system.web>

<pages>

<controls>

<add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

</controls>

</pages>

<compilation debug="false">

<assemblies>

<add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

</assemblies>

</compilation>

<httpHandlers>

<remove verb="*" path="*.asmx"/>

<add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" validate="false"/>

</httpHandlers>

<httpModules>

<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

</httpModules>

</system.web>