V1.5.0 to 1.5.4 update. Credit Cards not showing at checkout. Only money order.

[mc12345678]

The log had
Comm results: 60 SSL certificate problem: unable to get local issuer certificate
which to me is not caused by an invalid cc number. Or does it???????

Just want to make sure that you're chasing things for the right reason(s). The next obvious thing to do in that situation was to try some form of a valid CC (even in test mode) to see how the system responds... Yes if it worked then and not when invalid would seek resolution to that error message which doesn't make sense for an only invalid card, but if that was the response for an invalid card, worst thing about the response is that it is confusing but at least a purchase with an invalid card would not go through... :)

No, that has nothing to do with the CC number. It's caused by the server's internal SSL Certificate Authorities (not your shared certificate) not being up-to-date. Your hosting company has to fix that.

Try running http://your_site.com/extras/curltester.php to expose the CURL+SSL problems on your server, and let your hosting company take care of those ... that file is self-contained but will test CURL the same way ZC uses it, but without needing to run ZC to do the testing.

There is a remote chance that the curltester may not work on your setup as provided out-of-the-box, but it should work as is for the majority of systems. Please don't get frustrated as the reason it wouldn't is because of added security applied by the ZC team that the host hasn't allowed/doesn't offer working around/with...

[QuickBooksDev]

Failed same way with a valid cc #.

[DrByte]

Failed same way with a valid cc #.

The Error 60 is not a CC issue. It's a server configuration issue.

The difference between ZC v1.5.0 and v1.5.4 is that prior to v1.5.2 ZC was telling your server to ignore the authenticity of your SSL connection ... basically letting you get away with being hijacked if someone tried. That's why you're "suddenly" getting this problem.
But the fix to your problem isn't a Zen Cart issue. It's a server issue. Your webserver needs to get all its SSL Certificate Chains sorted out properly. This isn't the customer-facing SSL, but rather it's the backend server-to-server communication SSL infrastructure ... all within the control of your hosting company's server administrator.
That's why I told you to use curltester.php and have your hosting company use that as a tool to expose the problem while they make the appropriate changes to the server, testing repeatedly with curltester.php until they've fixed all their problems.

Chances are the problems are just extremely outdated server (software operating system) infrastructure.

[QuickBooksDev]

CREDIT CARDS ARE WORKING.

It was not a bad SSL cert but a bad pointer (pem) in the php.ini file.

Thanks everyone for your help.