After being able to transfer my own music on my F-02D, I wanted to set one of the songs as my ringtone but unfortunately, the songs were not considered to be available to be set as ringtone for calls/SMS...
"No music can set as ringtone" window pops up when I try to open my music list.

They play properly in the music folder but I'm unable to pick them as my ringtone.

Is there any proper way to resolve this?