I don't get this (YouTube problem).?

People can report your video for copyright infringement, and if so, youtube will mute the video's audio. I'm wondering if the copyright holder (or certain artists, companies, etc) regularly search for their intellectual property on youtube to deliberately assert their claim and protect their rights. Lesser known properties seem to remain unchallenged on their site.

Best you can do is try again, but you're risking the same result or perhaps a suspension - I really don't know what they do.

Even though this might not work for your particular video, they now offer a bunch of legal-to-use musics which they can place into your video, with the only cost being an ad for that particular music or something. Might be worth looking into later.

Well, in this case sometimes people say that they own the copyright and audio, so they can have the video and it won't be deleted! And if they find out that you did your account will be deleted. It has been experience by myself before. I've posted a video on my dogs and added audio, to it and it was matched to a third party. But anyways, if i were you i would just delete the video. There's no point they just mute the sound of anyways because it's owned by someone else.

that has happende to me onec and i redid it and hey let me through dont use the hole song

they could have permission from the owner to use it, or they havent got caught yet