Although I suspect I know the answer, trying to verify for sure what is causing my activation issue. Pertinent facts:

1) Computer was originally and still is Windows 7 Pro on the main C Drive. Fully activated for over a year with constant updates - no issues.
2) Used the MS Windows USB/DVD Download Tool to create a bootable USB drive with Windows 10 Pro installation files on it.
3) Successfully booted to the USB drive and installed Windows 10 on a separate hard drive in the same computer. However, during the early states of the installation it rejected my known-good key. Therefore I use the skip button to proceed and complete the installation.
4) After the various initial minor updates and a few reboots, have a Win10 running when I boot to that drive. (Obviously not fully updated since not activated).
5) Dual boot selection works fine.

Each time I attempt to activate Windows 10, I get the error 0xc004f050. Have tried unsuccessfully to get it to accept my key.

My suspicion is that because I am dual booting, unlike other people that upgraded on the same drive, there is no way for the activation process to verify things on my own computer, and if it's contacting Microsoft the Activation servers might be seeing that the key is already activated against "another computer". The cpu, motherboard, and network interface card are the same as the original activation- only the drive being used is different.

My hope is that someone here will have encountered the problem with dual boot systems, perhaps in the tech preview, and know of the proper solution.


PS: With Win10 there doesn't seem to be a way to 'phone for activation' and I suspect it won't matter anyway since it might just 'turn off' activation against my windows 7 installation....