OK that was the time I had a set of ladders linked by parenting to an empty so I could duplicate them then move them and rotate them as a block by manipulating the empty.
I found that if I ditched the parenting moved everything onto one layer then did a duplicate and move manually I was able to achieve the same function but without the accuracy of placement I would have had using an empty as a parent.
I then had loads of re positioning to do manually but with the structure now built I won't be needing any of that till I start reworking Noidrocca.
So any fix will still be useful just not imediately.