Thanks to Nick for replying!
The problem, this morning, turned out to be not rebooting after editing the rsmgr file.
What happens is, there is a white list for which scanners are allowed, and all others are forbidden. This is a change from 9.3 to 10.0. I think the idea is to stop malware addressing an imaginary scanner for some nefarious purpose.
So, YAST is supposed to set the whitelist to the scanner you have defined, in resmgr, and indeed it does, but if you don't reboot, for some reason xsane does not see it, and you end up with my situation last night, where the files all look fine, but your user account cannot see the whitelist from xsane or iscan, but root can.
The Suse materials don't tell you about rebooting, hence all the head scratching.
Suse has another thing which is very puzzling and not documented as obviously as maybe it should be. To access a network printer, you need to run lppasswd (probably not the exact command). Then you set up a user and password, which is completely independent of your system users. It is quite odd, the signon passwords do not work, including root's, and when you set up a user to manage the printers, you can set them up with a different password. There must be a dedicated user/password file somewhere, just for printers.
They must have some kind of reason for this stuff, but heaven help any users more naive than me!
Peter