Hello Glen,
You will get the warning message "The following audio or MIDI (or USB-MIDI) interface device(s) can't be accessed, but Hauptwerk is configured to use them ..." when you launch Hauptwerk if your computer's operating system is no longer reporting an audio/MIDI devices as being present that Hauptwerk was configured to use (based on the name that its driver reported for it). That will either be because the operating system isn't seeing the device at all (e.g. because it isn't switched on, or isn't connected properly), or because its driver has renamed the device.
When you see that prompt, first try:
- Leave its "Cancel launching Hauptwerk" option selected (as it is by default), then click its OK button to exit Hauptwerk.
- Shut the computer down.
- At the mains, completely turn off your computer, as well as all audio/MIDI devices and powered USB hubs.
- Wait at least 15 seconds.
- Make sure that your audio/MIDI device(s) and any USB hubs are still connected properly.
- Switch everything all back on again at the mains.
- Boot the computer and log in.
- Wait at least a minute for good measure, so that the operating system has had plenty of time to find any devices.
- Try launching Hauptwerk and see whether it no longer shows that warning [thus indicating that the computer is seeing the device(s) again].