I have a scene with a terrain, player, and a sphere. The sphere drops to a certain point when the terrain should become passable - BUT IT DOSE NOT!

#include <acknex.h>
#include <default.c>
#include "t_player.h"
//////////////////////////////

ENTITY* player="t_player";

ENTITY* terrain = "tester.hmp";

ENTITY* sphere = "ball.mdl";





function main()
{
level_load("xc1.WMB");

}


action down() //sphere drops to z-16
{

while(sphere.z>-16)
{
sphere=me;
sphere.z -= 3*time_step;
wait(1);
}} //this works fine


{
if(sphere.z<10) //this should be the trigger point //for the 'terrain' to go passable
{
terrain=me;
set(my,PASSABLE);
wait(1);
}} //But it does not work

CAN anyone help please? I need to make the terrain 'passable' or disappear from the scene altogether .
David