It used to be that whenever you took a screenshot of Apple's DVD Player application, you'd just get a black box where the video should be. At some point that had been replaced by this, much less confusing, yet equally frustrating error message:
Well today I discovered a fairly simple workaround for this “issue”. Just use the screencapture command line utility with the -i -s switches (to select only the area around the player, for example):
$ screencapture -i -s -c
… would put any screen selection into the clipboard, giving you:
You can of-course forget about all of this and just use VLC, but it might come in handy if you're trying to explain something specific about Apple's DVD Player application.