3d Bins

ave/spatial problem for obtaining a section averaging

Hallo everyone ,,
im running a simulation on LAMMPS and i need to have a section with averaging values of particles to compare it with other results ,,,so i need to creat a box in the middle of the box and then average the values of the particles within this BOX ,, the problem is that i cant define 3d bin !! i always get error message when i define more than one dimension in fix command !!

dimension 3
boundary p fs p

atom_style atomic
neighbor 0.3 bin
neigh_modify delay 5

# create geometry

lattice bcc 0.65
region box block 0 36 0 36 0 36
create_box 3 box
create_atoms 1 box

mass 1 1.0
mass 2 1.0
mass 3 1.0

# LJ potentialus

pair_style lj/cut 1.12246
pair_coeff * * 1.0 1.0 1.12246

# define groups

region 1 block EDGE EDGE EDGE 1. EDGE EDGE
group lower region 1

region 2 block EDGE EDGE 35. EDGE EDGE EDGE
group upper region 2

group boundary union lower upper
group flow subtract all boundary

region 3 block 17.75 18.50 EDGE EDGE EDGE EDGE
group midSec region 3

#region 4 plane 1 36 36 1 0 0
#group midSec region 3

set group lower type 2
set group upper type 3
set group midSec type 3
# initial velocities

compute mobile flow temp
compute sec all property/atom xs ys zs vy vx vz
velocity flow create 1.0 482748 temp mobile
fix 1 all nve
fix 2 flow temp/rescale 200 1.0 1.0 0.02 1.0
fix_modify 2 temp mobile

# Couette flow

velocity lower set 0.0 0.0 0.0
velocity upper set 1.0 0.0 0.0
fix 3 boundary setforce 0.0 0.0 0.0
fix 4 midSec ave/spatial 5 10 100 x lower 0.1 y lower 0.2 units box file FixBox.vtk ( HERE IS THE PROBLEM * !!)

* COMMENT : by compiling this i got ILLEGAl ave/spatial command
unless i delete defining of y dimension ( y lower 0.2 )

thankx for help !
Yaman