Is your ladder actually upright? Superku's line should work independently whether the player is in the middle or at any end of the ladder, because of the zero at the z value of the vectors.

Just an idea, replace "0" in both vectors by "player.z".

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt