Error 153 is a YouTube error message indicating that you don't have permission to view the video in the current context. It's very common across all platforms and applications.
That's likely because YouTube wants you to be logged in (with cookies, etc.) to view the video for tracking, ad revenue sharing, etc. Since you're not running within your normal browser context, Keynote doesn't have your YouTube cookies/login, and YouTube is (unhelpfully) telling you to go away.
If you own the video you're linking it to, there may be ways to mark the video as public and untracked (so unauthenticated users can view it), or you may have to move the content elsewhere. There doesn't seem to be a lot of direction from YouTube (at least that I've seen) on the specifics of how to avoid this message. It may be that any video can be viewed anywhere so many times, but popular videos (especially ones with ad revenue attached to them) may require login.