Thanks for the help DrByte.

The files are all there with their little green circles in the Downloads Manager.

I just enabled the error log on the server (wasn't activated originally); I then retried the checkout/download procedure again a few times and there is nothing showing up in the error log.

The SSL certificate was installed using the normal procedure for the HSphere Control Panel. When we say we disabled it to test the system, we ONLY disabled it from within the ZenCart system. We did not uninstall the certificate from the server. I guess I could do this - haven't tried it before; shoule be relatively easy to reinstall it?