You were right. For some reason I still don't really understand, I seemed to be able to put in a new IP address (very carefully) and all seemed OK, yet when I tried to print there was no communication and I found it had reverted to the old one again… Eventually I stopped fighting this and used the 'old' address anyway, and… 'success'. (Sadly this dawning took a while!) I'll have to try to find enlightenment in the 9100 instruction book, but it is so opaque.
Thank you for your kind help and encouragement.
I love the 'Mobius' clip on your site.