*update: Things did not go well. Although the server was re-configured to alleviate the problem, all it actually did was rule out the server as the main issue. We got a little further, but the problem looks to now be linked to the Virtualmin backend software running on Solaris OS. It's disappointing that I had over 10 site migrations in the last month go without a single issue (including DPUG which is virtually identical to APUG). DPUG has been on the new server for several weeks now. I am in talks with the Virtualmin support staff who have highlighted the issue as a bug that will be fixed at their next release. They are now hip to my suffering with this and with any luck will provide me an independent work around. I'll have to put another attempt off for a while to give you guys a break from these outages. Murphy's Law wins this week :/
Thanks again for your patience.