Grieg's music is all in the public domain, right?
I'm just making sure because I've uploaded one of my Grieg pieces to youtube and i already have a claim against it that says "matched 3rd party content". :\
I have faced this so many times over my son's recordings. There are a ton of music rights societies supposedly working on behalf of professional musicians. If YouTube's crude matching program "thinks" that your work sounds like a particular recording of Martha Argerich that is owned by EMI, it will allow EMI to slap that notice on your recording. This has nothing to do with Grieg being in the public domain. It's about 3rd party content.
Follow the dispute procedure and tell them that there is no 3rd party content. That it is your recording, of you, in your house, using your recording equipment. Then EMI will have to judge your claim. Usually, they release it. I have had to fight them repeatedly, and sometimes heatedly.
Once, I actually got Norman Lebrecht to publicly embarrass EMI on his website. Through that process, I found the email of a lawyer at EMI, and he "fixed it" for me. Of course, a few months later some other society (Orchard, I think) claimed the recording on behalf of a completely different pianist. And I fought them off. Never ending process.
Here's the Lebrecht involvement, BTW. It was fun! This is David's Boy, not Barenboim