inputenc Error: Unicode char ^^A (U+0001) not set up for use with LaTeX

I upgraded from an older Mac with High Sierra to a new Mac with Catalina and installed a fresh TeX Live package with TeXShop. Two of my old TeX files run fine, but the third is stalling even though I copied the exact same preamble to it. Can someone suggest a way to tackle this, or at least where I might search for a solution? Here’s my preamble:

documentclass{article}
usepackage{amssymb,amsmath} 
usepackage{graphicx}
usepackage[colorlinks=true, pdfstartview=FitV, linkcolor=blue, citecolor=blue, urlcolor=blue]{hyperref}
usepackage{CSTmacros}