I see that this was or might still be a common problem. If I render out some media (xavc-s) or any type, If I close that timeline and choose to drop a few clips in to start a new timeline I get that message every time with no playback available. If I close VP18 and start up again it is fine. Was this ever solved?
Full error message: An error occurred while starting playback. The request is not enabled for this device.