This is YouTube's way of telling you Keynote doesn't have permission to replay the video.
While anyone can upload a video to YouTube, and that video is available to anyone, there is a tipping point where the video is played back enough that YouTube track it for monetization purposes (ad insertion, playback credits to the author, etc.) In order to do this, YouTube needs to know who you are, which it does via various login/cookie mechanisms.
When the video is played back in Keynote, Keynote is not a logged-in user, and doesn't have your YouTube credentials, so YouTube tell you to kindly go away (via the entirely non-helpful 'error 153' message).
You don't have an option here as far as Youtube is concerned. YouTube are the ones deciding that they won't play the video to the current unknown/unauthenticated client, and Keynote doesn't know how to authenticate to YouTube.
If this is your video, consider storing it locally, within the Keynote presentation, rather than streaming it real-time.