group region error

hello dear
I’m simulating the a cubic which walls have been made by entering the code in lammps.the codes are below.when it run it shows below error.does anybody know where is problem?
thank you very much

variable T equal 398
variable V equal vol
variable dt equal 1
variable p equal 200
variable s equal 10
variable d equal $p*$s

variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable kCal2J equal 4186.0/6.02214e23
variable A2m equal 1.0e-10
variable fs2s equal 1.0e-15
variable convert equal {kCal2J}*{kCal2J}/{fs2s}/{A2m}

dimension 3
units real
atom_style full
neighbor 2.0 bin

neigh_modify delay 0 every 1 check yes


group hydrogen type 2
#group water type 1 2
group cu type 3
group oxygen type 1
group bottom type 3
group top type 4
group 3 bottom region wall #(or group stable bottom)
region cu bottom block INF INF INF 0.0 35 unit box
group 4 top region upper
region 4 upper block INF INF INF 0.0 35 unit box
create_atoms 3 region Cu

Check this command which is causing the error. Easy!

group 3 bottom region wall