It's OK "when all else fails read the instructions". It said re-install so I did that and it installed fine. I was a bit - well, a lot worried about having to re-register with the whole online thing but it re-installed perfectly, didn't ask to go online, and even hung onto my old P4 runtime and the Daz stuff I'd installed. A quick check of the face room - I'd been avoiding that! shows it works well... Feeling a bit daft now....