Forbidden error on homepage

We are occasionally getting a pop-up on our website homepage which just says ‘Forbidden’. The error report says it’s an ‘APBCT_AJAX_ERROR’ which I have seen many reports of on this forum.

I’ve only seen this happen on a couple of different computers though and it doesn’t appear all the time. If I clear cookies and cached site data on the computer/browser this happens on then the error goes away.

I’m afraid I can’t explain what causes this error, other than the only machines I’ve seen it appear on are also used to login to admin pages as well. When I login as admin the error goes away and then when I log back out again the message reappears.

Hope you can help!
Thanks,

Gordon

The page I need help with: [log in to see the link]