ERROR: non numeric box dimensions - simulation unstable

Hello everyone ;
I met a problem as below:
ERROR: non numeric box dimensions - simulation unstable
units real
dimension 3
boundary p p f

atom_style full
neighbor 0.5 bin
neigh_modify delay 0 every 1 check yes
timestep 1
thermo 10000
pair_style lj/cut/coul/long 8 10
pair_modify mix geometric
kspace_style pppm 1.0e-4
kspace_modify slab 3.0
bond_style harmonic
angle_style harmonic
dihedral_style fourier #hybrid harmonic
improper_style cvff
read_data graphenec.data

define groups

region lower block -6.00 28.00 -5.00 31.00 1.3 1.8 units box
region upper block -6.00 28.00 -5.00 31.00 81.69 81.7 units box
region middle block -6.00 28.00 -5.00 31.00 1.8 81.69 units box
group upper region upper
group lower region lower
group middle region middle
group 1 union upper lower
#region surface block -6.00 28.00 -5.00 31.00 0.3 10 units box
#group surface region surface
group BMIM1 molecule 2:130
group BMIM2 molecule 262:265
group BMIM union BMIM1 BMIM2
group PF6 molecule 131:261
group CT1 type 2
group CT2 type 3
group CT3 type 4
group CT4 type 5

set atom 1231 charge 0.0165
set atom 232
462 charge -0.0165

variable vol equal vol

change_box all z final -0.05 80.05 remap #x final 0 25 y final 0 25
dump m0 all movie 1000 BMIM0.avi type type size 1280 960 zoom 1.6
fix 20 all box/relax x 0.0 y 0.0 couple xy
min_style sd
minimize 1.0e-30 1.0e-30 130000 40000
#write_data graphenec2
reset_timestep 0
velocity middle create 300.0 4928459
unfix 20
fix wall all wall/lj126 zlo 0.05 0.07 3.55 8 zhi 80 0.07 3.55 8
fix CH all shake 0.0001 50 5000 b 3 5 7 9 13 15 18 a 2 3 5 6 7 9 10 11 13 14 15 20 21 23 26
fix lower lower rigid/nvt single temp 300 300 100 #x 1.0 1.0 100 y 1.0 1.0 100 couple xy
fix upper upper rigid/nvt single temp 300 300 100 #x 1.0 1.0 100 y 1.0 1.0 100 couple xy
fix aa middle npt/omp temp 300 300 100 x 1.0 1.0 100 y 1.0 1.0 100 couple xy
#fix de all deform 1 z final -0.05 80.05 remap v
thermo_style custom step temp press ecoul evdwl elong etail density vol spcpu
dump output1 all custom 500 dump1.lammpstrj id type x y z q
dump m1 all movie 1000 BMIM1.avi type type size 1280 960 zoom 1.6
run 200000

Hello everyone ;
I met a problem as below:
ERROR: non numeric box dimensions - simulation unstable

this means exactly what it is says: your simulation has become
unstable for some reason. in fact so much, that the pressure was
computed to be not numerically representable and thus the npt box
update has resulted in similarly not representable numbers. you have
to check your system configuration and your input parameters for
unphysical settings.

axel.