This is normally due to the fact that you have passed the URL for you company logo to ePDQ, via the osCommerce admin control panel, and that URL is not SSL secured (https).
Any image URL given to Barclays ePDQ MUST be hosted on an SSL server (with an https address) as the ePDQ system is SSL secured. If not then your browser (Firefox, IE, etc) will complain.
Your ISP should have a facility where they can host an image for you on an SSL server.
