PHP released a new version earlier, and I thought I'd get the servers updated. Installing the new version on my development machine produced no problems, so I installed it on all of the servers that required it. All except the server that houses the hpHosts forums and fSpamlist blog, have taken to the new PHP release without issue.
I've already tried rolling back to the prior version that was installed, but the forum software is being a pain, and the fSpamlist blog software, keeps insisting the MySQL extension isn't available when it is, so I'm stumped for now.
The server needs re-built anyway however, and as I'm shattered, I've left it for now, and will see to it later today.