Pad not found on Windows 8.1
There is an issue with Windows Enhanced Power Management which was modified in Windows 8.1.
All STU devices work without a problem with Windows 8.0.
Windows 8.1 changed Enhanced Power Management and as a result the STU pads are powered off when not in use.
This results in the STU pads being unavailable to the SDK software and the user will see errors such as "pad not found".
Recent models, the STU-430, 530, 540, are unaffected by the Enhanced Power Management and can be used without a problem because they use a different type of USB interface.
To prevent the other models being powered off (STU-300/430/500/520) install the STU tablet driver - this is not normally needed for the STU-300 but it will prevent the tablet being powered off.