In the end the solution was very simple, however the way in which I found out it was simple, was not simple.
Firstly, let me remind you the mac in question is a production machine, therefore I can’t afford to do anything wrong. So I had a plan.
I have a spare G5 (lucky me) so I decided to Carbon Copy Cloner the spare Mac (Mac 1) to a disk image on an external. I’d do the same to the Mac with the MobileMe problem (Mac 2).
It would then be a simple case of installing Mac 2’s disk image to Mac 1. I could then troubleshoot this Mac as much as I needed until the problem was solved.
Well this bit sounds simple but the cloning took ages; a day and a bit later I was set.
So I ran Onyx to clear all caches. After a restart – problem remained.
So I reinstalled the 10.4.11 update – and this solved the problem.
A short while later the production Mac is MobileMe’ing happily.
Why did MobileMe die? – Who knows?
Am I now happy? – Not really. When something goes wrong with a Mac I expect the answer to be a logical progression of testing and narrowing down the problem.
In this case, nothing made sense. The problem didn’t seem to have a logical solution, and the only thing that worked was overwriting some files with a combo updater.
This isn’t very Mac-like – and it’s that aspect of this that worries me a great deal.