Fix SSL checkout - virtuemart - Joomla

I have a joomla 1.0 site with virtuemart, we are using a shared ssl certificate which works fine. we have installed a ssl certificate for our own domain name which works and brings up the site fine. But when you go to checkout, you get redirected back to the home page. I have changed virtuemart ssl URL back to the shared SSL certificate to allow checking out Your job is to make the site work with the new installed SSL certificate, the site uses open SEF. Checkout and links are to work, no errors through checkout process. I am after a fast turnaround ( 0 days ) and can not have any mistakes :)