Using Music On A Slideshow On Youtube??

[lucyshandbag]

I have made a few slideshows for friends and put them on YouTube. Every one of them has a song with it but some won't let them play on a mobile device, they say "cannot be viewed on this platform" or something like that, whereas some of them are fine. When looking on the Internet for a reason for this it seems it's something to do with copyright issues with the song. Is this right? And why does it only happen to some of them and is there any way around it? Any advice would be appreciated. Thanks

[chrisgel]

Use some copyright - free music from sites such as this
http://www.freeplaymusic.com/