er...strummer bad on certain song????

[Elegy]

it seems as if my strummer randomly misses notes on Casey Jones. Every other song it seems to work, but even when I'm spot on, and the right buttons are pushed down, i seem to miss the note on this song.

Is this possible?

(Also, I can understand if I'm messing up a lot, but it's an easier song and i don't see how i could mess it up)