The path can be changed as follows.
Use the following command, in the MATLAB command window, to see the path:
This path cannot have any of the offending characters in folder/filenames (e.g. in my case, Dropbox hijacked my Documents folder and used spaces and '()' in the name of that folder). This does not include the '/' symbols in between folders.
Change the folder/filenames as necessary with
And off you go. Thanks so much to Adrian at HQ for providing clear and useful support by email.