Hi Richard,
It is probably best for now if you can work from cvs head, because I now remember making some minor changes in acs-core to get register referrals from ecommerce to redirect back to ecommerce.
Also the oacs-5-4 branch of ecommerce is looking like a tag in cvs. I probably created the wrong label type or label name for ecommerce when I tried merging the head version on oacs-5-4 branch a few months ago.