If your web application using Microsoft Ajax (Ajax Control Toolkit), then you probably encounter common unknown javascript error as following:
Sys.InvalidOperationException: Handler was not added through the Sys.UI.DomEvent.addHandler method.
Cause:
Unknown handler error in MicrosoftAjax.debug.js
Resolution:
To ensure your server not prompting this debug message on your test or production server, just set debug=”false” in web.config. By doing this, ASP.net will not automatically include MicrosoftAjax.debug.js into one of the resource.axd
