Queued videos opened with "Open Video in Popout Player" tries to open the video with the queue playlist (which is not supported).

[Wicke2d]

When a video is in a queue there are two options: Open Video in Popout Player and Open Playlist in Popout Player.
The latter option would understandably try to open the video with the queue playlist, although it fails because queues are not supported.
The former option triggers the same "This video is unavailable" error, although it is supposed to open without playlist, simply by omitting everything in the URL from &list= onwards.

Sidenote: There exists a simple Firefox Addon for opening a video without playlist.