Short version of the reason for it: A security update broke part of the PHP installation on the live server that went fine on the test server.
The longer version is overly geeky, but suffice to say an important shared library (the *nix equivalent of a .dll) used by PHP but was at a fairly old version got updated as well and PHP didn’t like it too well because some key parts were changed so I had to reupdate PHP to fix it.
Re: Sorry about the down time between 1:40 and 2:24 AM Central Time
Oh yeah,
I remember the fun of updating php on production servers, and afterwards finding that a number of customers websites only displayed a blank white page.
Had similar issues with a major release upgrade of mysql. Having to down grade to keep customers happy is a pain, but better than having a mass walkout so to speak.
Glad it did not take you too long to sort it out.
Re: Sorry about the down time between 1:40 and 2:24 AM Central Time
We won’t discuss the horror of trying to do MySQL updates on this server. Let’s just say there is a very good reason I run updated versions for at least a week on an alternate port before replacing the currently running version 
Normally the update procedure I use for PHP would have caught the problem. I have no idea why it failed this time, but to be on the safe side I’ll be using a similar procedure to what I use for MySQL from now on