oscommerce shared ssl problem

I currently run 2 oscommerce stores, [login to view URL] and [login to view URL] [login to view URL] works fine as it has its own ssl certificte, but I'm having a problem with the linspiration site which uses a shared ssl certificate. All is fine with the site, so setting up accounts, adding products, etc, but as soon as you switch from http to https, all info is lost from the shopping cart. The normal domain is [login to view URL], and the shared certificate uses the domain [login to view URL], and I have a feeling it's something to do with when it switches from one domain to another. [login to view URL] has had a sligh modification around line 41, which was lifted from the oscommerce forums and helped to give a closed padlock, but when I removed this modification the site still didn't work as hoped and the padlock was broken. Thought I shoul mention it as it mite be relevant. I've also attatched the file. I'm sure it's a very simple matter, but I have neither the skill, or patience to learn it at the moment.