So I'm back up and running, thankfully. I deleted the newly created node_modules folder then copied over the node_modules folder from the course on my old PC.
grunt build is now working with no errors.
What I did notice was that the old node_modules folder has 15,790 files in it, but the newly created one only has 11,823 files. I'm rather clueless as to what all these files are but I'm guessing the change in the makeup of the node_modules folder since the course was orginally created (May 2018) had caused this problem.