There are several issues that you need to look out for when employing user interaction events on line graphs. We'll detail them here:
Events fire only on bullets, not line itself
No bullets - no events.
But what if I don't want to display bullets? There's a workaround: enable bullets but set their alpha to zero, so they remain invisible but will still trigger interaction events:
graph.bullet = "round"; graph.bulletAlpha = 0;
Rollover bullet might be obstructing the actual graph bullets
ChartCursor as well as AmBalloon instances can also display their own rollover bullets that when drawn on top of graph's bullet will prevent events from firing. Make sure those are disabled:
chart.balloon.showBullet = false; ... chartCursor.bulletSize = 0;