<<...that one statement tells me it's being blocked by a firewall, or something.>>
I will agree with the "or something."
No single firewall exists across two different OS installations, one Windows 7, one Windows 10. I'm using the same antivirus / firewall package on both computers, the other Windows 10 computer, DeskScapes works fine.
The only thing common to the two OS's on the computer in question is the hardware itself. And yet nothing else is blocked in either OS?
We have to be looking at a bug, here. I'm not saying the bug has to be in the DeskScapes program--could be some peculiarity in chipset driver, NIC driver, firmware, or some combination.
I've compared Ethernet adapter settings between the system that works and the one that doesn't, they are identical. Also compared environment variables, tried turning UAC on / off, changed the computer name, did a reinit on the network...no difference. It's running an unmodified HOSTS file. I also uninstalled the antivirus /firewall package, and that made no difference either.
Every browser on the system can go instantly to wincustomize.com with no delays at all.
I'm not sure it can be made to work on this hardware, or maybe this specific combination of hardware. It's got me stumped.
I don't know if I ever will, but I would very much like to figure it out someday.
If I ever do, I'll post the solution here.