I am getting a exception in the gecko.xml file

<bindings id="activeui"
xmlns="http://www.mozilla.org/xbl"
xmlns:html="http://www.w3.org/1999/xhtml"
xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

exception
Severity Description Resource In Folder Location Creation Time
2 cvc-elt.1: Cannot find the declaration of element 'bindings'. gecko.xml cms-web/WebContent/css/xp

does anyone know why?

Thanks