invalid fix style for diffusion example

Dear users,

lammps gives me the following error when I  run the simulation "in.msd.2d" in the
example folde of DIFFUSE in lammps. I checked the manual and the mailing list, this
error seems to be caused by missing package. I think here the "invalid fix
style" is talking about "rigid", but I installed the package RIGID and
compiled it, which is successful. But I still get
the following error message. 

Would you please tell me which package I should install to fix that error?

variable x equal 40
variable y equal 40
variable rho equal 0.6
variable t equal 1.0
variable rc equal 2.5

units lj
dimension 2
atom_style atomic
neigh_modify delay 0 every 1

lattice sq2 ${rho}
region simbox block 0 $x 0 y -0.1 0.1 create_box 1 simbox create_atoms 1 box pair_style lj/cut {rc}
pair_coeff * * 1 1
mass * 1.0
velocity all create $t 97287
fix 1 all nve
fix 2 all langevin $t $t 0.1 498094
fix 3 all enforce2d
thermo 1000
run 5000
unfix 2
reset_timestep 0

compute msd all msd com yes
variable twopoint equal c_msd[4]/4/(stepdt+1.0e-6)
fix 9 all vector 10 c_msd[4]
variable fitslope equal slope(f_9)/4/(10
dt)

thermo_style custom step temp c_msd[4] v_twopoint v_fitslope

only need to run for 10K steps to make a good 100-frame movie

thermo 1000
run 100000

dear sara,

by now you should have recognized that ignoring advice been given and instead repeating variations of the same (pointless) question over and over again without any indication of having put in the effort to actually understand what people have suggested. this leads to people considering you as a hopeless case and ignore you. acting as if you are entitled to somebody solving what ultimately amounts to your problem is just making matters worse.