We'd need to see more of the code but a stab in the dark,

you've created a boolean pointer somewhere and are storing the entity in this (won't show any problems in the compiler) but the BOOLEAN data type doesn't have a .x property, make sure that cylinder is an ENTITY pointer.

basically what i'm trying to say:
Code:
///////////////////////////////
#include <acknex.h>
#include <default.c>

///////////////////////////////


BOOL bool_temp;


void main(){
	
	BOOL bool_temp;
	level_load(NULL);
	bool_temp = ent_create(CUBE_MDL, vector(1, 1, 1), NULL);
	
	bool_temp.x = 1;
	//vec_set(bool_temp, vector(1, 1, 1));
	
}


change to:
Code:
///////////////////////////////
#include <acknex.h>
#include <default.c>

///////////////////////////////


ENTITY* ent_temp;


void main(){
	
	level_load(NULL);
	ent_temp = ent_create(CUBE_MDL, vector(1, 1, 1), NULL);
	
	ent_temp.x = 1;
}


or .x inside the entities on function would work
Code:
///////////////////////////////
#include <acknex.h>
#include <default.c>

///////////////////////////////


action move_me(){
	while(me){
		my.x += time_step;
		wait(1);
	}
}

void main(){
	
	level_load(NULL);
	ent_create(CUBE_MDL, vector(1, 1, 1), move_me);
	
}
Hope this helps (and makes sense)


ENTITY*