Page 1 (Parallel Process):
Graphic: None
Conditions: None
Commands: Sound effects, graphics, turn Self Switch A ON
Page 2 (Action Button):
Graphic: Rock
Conditions: Self Switch A = ON
Commands: None
Erasing Events, as diagostimo said, only removes the event for that instance of the map. Leaving the map and returning to it will bring the event back. Unless you know how to access your map files and remove events from them via scripts, there is no permanent way of removing events. You must use switches (or some other form of condition) to prevent events from triggering twice.