Song ends early?

I made song into sm and it ends and blacks out before the whole song is done. I still see the arrow coming up but it blacks out. How do I fix this.

Is there a break in the song? Or does it just randomly stop? Does it stop in the same place every time?
Also what would help is if you posted the song, with the sm file, mp3, and everything else, on this forum so I could look at the file and tell you what's wrong. It could be many things.