This seems to be due to a compatibility issue between the vJoy driver and other HID (e.g. joysticks, game pads, mice, keyboard, trackball, etc)-drivers. More specifically – it seems to be an issue with USB-devices that has been installed under Windows 7 or 8 and then been brought along during the Windows 10 upgrade.
It should be possible to detect these USB-devices by opening the device manager and select “Show hidden devices” under the “View” menu. Devices that has “…not migrated” under events seems to be the main source of problems. Try uninstalling these devices, reboot and let Windows 10 find new working drivers (or download and install them yourself).
You can read more about this on the vJoy forum: