Well that could mean a few different things:  YouTube took the royalty payments for the music and images out of what they are paying the partners.   They have opened them selves up to a lawsuit.  Or (and I think this is the most likely) the partners aren't payed for videos that have copyrighted stuff in them.  Based on what I've read/seen there is some option partners have that makes the video a paying video or a non paying video.