This is a follow-up to my previous post. I continued to try to fix the problem without consulting Sony Support. In the process, I managed to screw up some Windows settings. (Don't ask.) I know almost nothing about Windows or computers but somehow managed to fix those problems. I then uninstalled the HAP Music Transfer app, downloaded it, and reinstalled it. That seems to have fixed the problem, as my computer is now transmitting music files and data to the HAP S1. It's going to take at least 24 hours to complete the process; only 10350 files to go. The only glitch so far is that the HAP Music Transfer app has twice stopped on its own accord. So, I started it again, and both times it seemed to pick up where it left off, or at least I hope it did.
I've been pretty happy with the HAP S1 overall, but this is the third time that the Music Transfer App has become corrupted and inoperative, and I've to uninstall and then reinstall.
When I purchased the HAP S1, I thought that one of its advantages was having an internal hard drive, which I thought would provide more reliable performance than streaming. I'll certainly reconsider that if and when I buy a replacement. If I again purchase a machine with an internal hard drive, I'll buy one that allows for direct loading of music, in addition to either Ethernet or wireless loading.
So, Lepanto, if you're still having a problem, you could try uninstalling the HAP Music Transfer App and then downloading and reinstalling it. Good luck!