This post is to tie up a loose end and share what the solution was.

PG Music support was not able to replicate the issue I was having, but did offer some suggestions. Unfortunately they did not help.

Out of frustration I replaced the C:\bb\Demos\MIDI Style Demos folder with a fresh copy from the installation hard drive and the issue disappeared.
I don't understand how 2 separate PCs suffered the same corruption, but replacing that folder did cure the 'Not Found' problem I was having.

Thanks again for the suggestions made here.