Thank you - yes, I really appreciate your help and hope I've not come across as otherwise.
As I said, I'm really disappointed the program that has met my needs so well for so long suddenly does not any more. In the last three weeks I've spent more time stretching my fairly non-technical brain in trying to get it working (as well as having to learn how to get the job done in Cubase) than I have working on my projects.
PT support have offered to have one more go with a remote access session, which I hope they will, but if that gets us nowhere then I'm resigned to the fact that I'll just have to use it for anything MME is OK for, but I'll have to do ASIO tracking and mixing down in Cubase.
I have thought about asking for a refund but it's not a great deal of money and I'm reluctant to admit defeat in the hope that one day it will come right.