Sorry, I was away for a bit.
No joy with the suggestions in the link, thanks for your efforts.
I'm on a PC, not large files eg I open a new blank workbook, save it as "test" , then File-->Protect workbook--->Encrypt with a password
If I create the password 123, save & close. then I open it, type in password 124, I get the incorrect password message & instead a new Book1 opens.
This is a relatively recent development, though it might be something new with a recent upgrade but internet searches don't show anything....anyway, it's just a minor irritant.