Download music from computer to mobile is failing..

[plethota]

I was wondering if anyone could help me with a problem that I have on my phone.. I downloaded some music from youtube in a mp3 file, that have worked plenty of times after putting them over to spotify.. I just tried to put 5 new songs from my computer to spotify, but 4 of them failed.. One song worked and the other songs only works on my PC, not on my phone htc galaxy s2 (if that helps..) So I was wondering if anyone can help me get those 4 songs to work on my phone as well.. Don't know what I did wrong,    because all the other songs I have moved the same way worked..