SSL / https://. I got it working.

Of course you need to have an SSL certificate installed on the domain where the cart lives.
My SSL provider does not allow sub-domains or folders.
Only the domain can have an SSL certificate.

I changed the url in the admin/config.php file to reflect the https:// on lines 8 & 9.
(not the root config.php)
I selected "use SSL" in the settings/server.
In Manage Stores/my store/ edit, I changed the store url to https://.
(I read this on someones post, but I can't remember who)

DUH!
It was almost too easy.

Now my merchant account provider will scan the site for the https://
and we are in PCI Compliance
since the Authorize.net module does not store card info.

Mark