Thanks for the suggestion. I tried it. It doesn't help. If the ICE file is there then Calibre breaks - even if everyone in the worls can do whatever they like to it. Even if it's brand new after a reboot. Even if I show it nice pictures of ponies. Only if I delete it does Calibre news download work.
It seems as if the problem lies at a lower level than I'm competent to address. But killing the ICEauthority file definitely works and so far, so does everything else.
Since this is the first thing I've found that does work I think I'll stick with it until a more elegant solution comes along
Thanks again for your time