This one gives me a Crash in sys (system)
why?

*****************************************
var j;
var i;
ENTITY* door2;
action pass_door_asansoor()
{

door2=my;
set(my,POLYGON);
my.skill10 = my.z;

while (1)
{
while (my.z < my.skill10 + 180)
{
if (vec_dist(my.x,guard1.x )<100 )
{
i=1;
j=0;
}

if(my.z < my.skill10 + 180 && i==1 && j==0){
my.z += 20 * time_step;
}

wait (1);
}

while (my.z > my.skill10 )
{
if (vec_dist(my.x,guard1.x )>280 )
{
i=0;
j=1;
}

if(my.z > my.skill10 && i==0 && j==1 ){
my.z -= 20 * time_step;
}

wait(1);
}

wait(1);
}
}
****************************************
can you help me please?
thanks