Google Analytics failing when customerror used on homepage

I've got customerror installed and have just put the Google Analytics module on.
GA is not picking up the fact that it's installed, even though the javascript is showing on the homepage.
I'm using customerror to control access to a site, showing a 403 page on the home page if not logged in.
Is there a simple way of using customerror in this way so that it will allow GA to function as expected?
To view the source code of the site, see www.thule-net.com
Thanks.