YouTube is notorious for automatically removing videos containing copyrighted music, even if it's just playing in the background. It has some sort of algorithm to scan videos, then flag them as having copyrighted music. I think nowadays they'll let you keep the video up as long as you aren't earning money from it, though.

Formerly TN Lone Wolf

"We are only as strong as we are united, as weak as we are divided." - J.K. Rowling