Marketpress plugin checkout issues — SSL???

I have Marketpress installed on and when you click on “Checkout” after putting an item in the shopping cart, it gives a red flag about the SSL certificate being signed by a different domain. Is there a way to disable it going to a secure connection? is the host which is what it says the certificate is signed by, but I need that to NOT happen. Any hints?!?! Need to take care of this ASAP! Thanks!