Using the quick start sample provided by Google I\'ve been able to get Sign In for Web Apps to work in Chrome and Firefox. However it fails on Internet Explorer (version 11.
Try to load your scripts from other place than google. According to this Question (Preventing "SCRIPT5: Access is denied" error in IE) that "SCRIPT5: Access is denied. " error is a way Ms has to 'protect' the user against XSS.
So, try to download https://apis.google.com/js/platform.js and use it form your local server instead.