I suspect it was a system problem, but don't know why. It's a server OS for goodness sake--it of all systems should be able to handle serving files. I did find that sometimes near the end of my tests, the PC would start reporting limited network connectivity. If I toggled the connection, it would sometimes work for a little while longer. I ended up with a batch file which restarted HFS and reset the IP every six hours, which did help. As I said, though, these resets worked for progressively less time until I rebooted the PC.
I had some basic security software, but nothing too aggressive, and nothing I hadn't used before. I don't think it was to fault.
HFS is still running without a hitch almost a week later on Win 7 HP. I have more security on it this time, and still no problems. For now, I'll just continue to wait and see how it holds out.
Oh, one last thing, whatever part of the BIOS/motherboard which handles time seems to be out of whack. Every time I check the server it shows a different but entirely wrong time, and it's set to update every few hours, too. It has been doing this for all systems which I have placed on it. I can work with this it, but I don't know if this might have been wreaking havoc on HFS for some reason before. If so, then why not now?
I hate intermittent "ghost" problems!