Ultimate Facebook - Unable to Login

Hi All,
I am unable to login using "Login with Facebook".

The following error shows up in a popup window. This is the result if already logged into facebook, tried on two of my sites.

Given URL is not allowed by the Application configuration.: One or more of the given URLs is not allowed by the App's settings. It must match the Website URL or Canvas URL, or the domain must be a subdomain of one of the App's domains.

If not logged into facebook the popup shows with the facebook login screen, once logged in it returns the above error also.

These were working up to today. I have check the app at facbook and all settings.

No theme changes have been done, currently running upto date versions on all plugins and wp.

Appreciate any assistance with this one, thanks.