can't seem to download your example file right now, but here's how i would do it.
create 2 image points for your ladder. (1 = top of ladder, 2 = bottom of ladder)
On mouse click on object "ladder".
(sub event) system compare 2 values distance(player.x, player.y, ladder.ImagePointX(1), ladder.imagePointY(1))
< distance(player.x, player.y, ladder.ImagePointX(2), ladder.imagePointY(2))
This checks the distance between the player and the 2 image points. If image point 1 is closer to the player, then you know he's near the top of the ladder, if point 2 is closer, then he's closer to the bottom of the ladder.
Next, move the player automatically to the proper imagepoint location, then play the ladder climbing animation, while he automatically moves the other image point.