Twenty-four hours in it appears I now have a disk migration working. Usually it's a simple task. Unpack the machine and fire up Migration Assistant after going off to make and drink a few cups of coffee and presto the new machine is up and running.
Well that worked for the first many dozens of processors in the collection. This time, however it was not to be so simple. Each time Migration Assistant would run it would exit with the same error message. Read more about Trials and time machine