Make a new script in Advanced mode with the same options, source(s), destination, and selectors as the script you are worried about and then "Preview" to see what's going to happen.
Thanks Lennart. I got it working by uninstalling Retrospect, downloading the archive copy again, and reinstalling. I suspect that the cause of the problem was that I had not downloaded the correct version; perhaps I had downloaded a non-USA version. In any case it is working now.