Help with a custom cursor

1

I am trying to get a custom cursor working in MX - The cursor is a fine line the length of the movie.

I am using this piece of code from a tutorial:

onClipEvent (load) {
Mouse.hide();
startDrag(this, true, L, T, R, B);
}

My page has a number of movielips, some are masked and can be unmasked when the mouse rolls over them. This code works when there is only one movieclip on the stage, But when I add multiple clips with masks the cursor does change to the line, but the line freezes when I attempt to roll over the masked movie to unmask?

What am I doing wrong?

Thanks