Ken and David,
Thanks I finally managed to find a forum post to that effect and sure enough when I checked the two servers, they were off by about 17 seconds. The Moodle code dictates a maximum of 15 seconds apparently...thus the error. When I synced them (almost) everything was back in order.
One of my servers (the one that has the destination Moodle site) is behind another with Apache functioning as a proxy forward to allow the second server to be accessed on the same IP. I guess I need to set it up so it can sync with an external clock to keep it in line with other servers.
Thanks for your help.
P.S. David, I've contacted Martin about someone from Moodle HQ coming to our Moot in Japan next February and you were highly recommended by one of our members. I know Martin is very busy so he may not have seen my message. Any advice as to how I can get in touch with him?