Done. What I found was that the 7-zip file defaulted to using no pathnames whereas previous versions defaulted to using stored pathnames. Not sure why the difference. A clean directory and switching to using saved pathnames solved the problem.
BTW, if unzipping over a previous nightly is a problem, it might be useful to say this on the How to Use a Nightly Build page in this forum. Specifically, it currently says:
5. Upgrading the nightly
If you followed the advised approach your compilers, debuggers are separated from CB itself. This means you can delete your CB nightly install directory without any harm, since your user settings are stored in your user profile directory (eg. default.conf), and unzip the new nightly build, or you can unzip your new nightly build on top of your previous nightly build. In the latter case be sure to overwrite all files !!!