Thanks!Ryu Sei wrote:
Songs with not enough rights to use can be removed by artist/copyright holder's request. If it happened after the map is ranked, the map will have no audio file to play. Sometimes, the restriction comes from system rather than manually done, such as when you're trying to upload maps using DJMAX songs; they're automatically denied from submission system.
It's always a good idea to ask to the artists first whether you can use it for osu! or not. Read here for more information: wiki/en/Rules/Content_Usage_Guidelines
Don't get discouraged if the song you wanted to map is not allowed to be used in osu!. There are other songs waiting for you to map out there! If that's a hassle for you, you might want to check Featured Artist section, where these songs are completely allowed to use in osu! for free, without worrying copyrights.