I thought that I was going crazy.

I literally spent the last 2 hours trying to figure out what was wrong.
1. I reinstalled (and even wound back) my NVIDIA drivers.
2. I mucked with firewall settings.
3. I installed and uninstalled every version from v5.30 to v5.33.
4. I wiped out traced from my registry, program data, etc and so on.
Not a single darn thing worked. I was beginning to think that it had something to do with a Windows 10 update. I came here... Solutions.
1. The time rollback trick works
2. Renaming the iray directory also works
FWIW, v5.25 installs and works just fine too. For those of you starting a new project, that might be a viable temporary solution too. The problem is almost certainly connected to iray since that wasn't introduced til v5.30.
For the techies who might need to know my current setup....
CPU: Intel Core i7-4930k hexacore @3.4GHz
GPU: NVIDIA GeForce GTX 950 2GB (361.43 drivers)
OS: Windows 10 Pro 64-bit (v10.0.10586)
LICENSE TYPE: Indie
At least there are workarounds. Small blessings, right?