This seems to be due to a compatibility issue between the vJoy driver and other HID (e.g., joysticks, gamepads, mice, keyboards, trackball, etc.)-drivers. More specifically, it seems to be an issue with USB devices installed under Windows 7 or 8 and then brought along during the Windows 10 upgrade.
It should be possible to detect these USB devices by opening the device manager and selecting “Show hidden devices” under the “View” menu. Devices that have “…not migrated” under events seem to be the main source of problems. Try uninstalling these devices, rebooting, and letting Windows 10 find new working drivers (or download and install them yourself).