Thanks to everyone for helping me out. I loaded a trial version of MC28 on my PC and everything worked properly immediately. I've decided to switch platforms. My Mac Mini is now sitting in a closet...
I now have a few new questions:
Will my Library from MC for Mac work with MC for Windows, or do I have to build a new Library? I am not worried so much about re-importing everything (done), but I don't want to have to remember how to do all those things I've only done once like configure where my album art is stored, pointing MC to where I keep my TV show art, and other various settings.
When I started the MC28 trial version and created a new Library, a portion of my meta data seems lost. The most obvious and immediate example is song/ show ratings. Is that a problem with my new Library, or is it a problem with the files I copied from my external hard drives to my NAS? Or is it something else?
This is for the MC staff: can my license be converted from Mac to Windows? We will not longer have any Apple products in our house, so I don't need a master license.