My nokia 6300 won't let me set the ringtone to a song from my music file?

[NatalieLondon]

It used to be able to, but now for some reason it just stopped no matter how small the file size of the song is, it won't let me set it as the ringtone...it usually says file size too large...i don't know what to do..and im sick and tired of the dumb ringtones that came with the phone!!!!!!!!!!!!
please please please help!