Query regarding lost atoms

Respected Sir,
I am using this program .So,the problem is it shows the following error
Lost atoms: original 26449 current 26424 (thermo.cpp:389).Can anybody tell me what is the problem in the command.

units metal
boundary p s s
atom_style full
neighbor 2.0 bin
neigh_modify delay 5

create geometry

lattice fcc 4.090

region box prism 0 60 0 10 -5 5 1 0 0
create_box 3 box
create_atoms 1 box
mass 1 107.87
mass 2 107.87
mass 3 107.87

define groups

region 1 prism 0 10 0 10 -5 5 1 0 0
group lower region 1
region 2 prism 10 50 0 10 -5 5 1 0 0
group upper region 2
region 3 prism 50 60 0 10 -5 5 1 0 0
group middle region 3
region ind union 3 1 2 3

pair_style eam
pair_coeff * * Ag_u3.eam

change_box all xy final -6.15 z final 0.0 1.0 boundary p s s remap units box

initial velocities

compute pa all displace/atom
compute pp all reduce sum c_pa[1] c_pa[2] c_pa[3]
variable vv equal (c_pp[1]+c_pp[2]+c_pp[3])/3

compute pa1 all stress/atom
compute pp1 all reduce sum c_pa1[1] c_pa1[2] c_pa1[3]
variable vv1 equal (c_pp1[1])+c_pp1[2]+c_pp1[3]/(vol)

compute peratom all pe/atom
compute pe all reduce sum c_peratom

variable delta equal vol/(ly*lz)
variable strainn equal (v_delta-245.64295)/245.64295

fixes

fix ind all nve
fix 2 middle temp/rescale 500 0 100 100 0.5
run 100
unfix 2

run

timestep 0.003
thermo 2000
#thermo_modify temp new

thermo_style custom step press vol lx ly lz v_delta v_strainn v_vv v_vv1 c_pe temp

dump 1 all atom 1000 dump.crack1
dump 2 all image 1000 image1..cfg type type zoom 1.6 adiam 1.5
dump snap all cfg 1000 dump.config.
.cfg id type xs ys zs

dump_modify 2 acolor 2 green

run 25000

Regards,
Ritesh Satwani

The errors section of the manual explain that error (and all others),
and in this case what you should look at in your model and script.

Steve