Ultimate Branding - Admin Bar - Logo replace returns 403 error

Ultimate Branding - Admin Bar - Logo replace returns 403 error

I get a ...

403 page, Access to this resource on the server is denied!

when trying to replace the Wordpress logo on the Admin Bar tab with a custom logo using the Entry Title (text or image) entry box field.

I have checked and double checked the link and can access the link address via a browser but it keeps returning an error.

If I enter text it is OK.

Hope to hear from you soon.
Thanks,
Simone.