It looks like your purchased certificate uses a different CSR than the one on your account.
I can't register the certificate because they don't match and I don't have the private key used to produce that certificate that you sent me.
I've gone ahead and turned off SSL in the meantime to allow your site to function without causing interruption to your orders for now.
You will have to contact Dreamhost and have them generate a new certificate using the CSR I've included in the private area. Once that is done, send it to me and I'll get it installed right away.