Why: Sorry, an error occurred. Your video edits could not be saved. – YouTube
If you are trying to edit a YouTube video under the copyright notice area, you may receive a message that prevents you saving your video after attempting to erase or mute part of your video audio.
Typically, this YouTube message displays if you edit multiple videos concurrently. Wait at least a few minutes before trying to edit another video.
All else, YouTube servers are likely overloaded and suffering heavy user usage – this is very common to happen recently on weekends. You may also be experiencing slowness generally on YouTube and receive the dreaded message: 504 That’s an Error