LAM: mpi problem with gromacs

Dear lam users,
After requested installations and configurations  for gromacs-parallel on RHEL 4.0 ,
 when I run gromacs with this command:
mpirun -n 2 mdrun_mpi -v
I have this message:
69 pc239:/home/mario/d.dppc> mpirun -n 2 mdrun_mpi -v
MPI process rank 0 (n0, p512) caught a SIGSEGV in MPI_Comm_size.
MPI process rank 0 (n0, p9663) caught a SIGSEGV in MPI_Comm_size.
Rank (0, MPI_COMM_WORLD): Call stack within LAM:
Rank (0, MPI_COMM_WORLD): ; - MPI_Comm_size()
Rank (0, MPI_COMM_WORLD): ; - main()
Rank (0, MPI_COMM_WORLD): Call stack within LAM:
Rank (0, MPI_COMM_WORLD): ; - MPI_Comm_size()
Rank (0, MPI_COMM_WORLD): ; - main()
I don't understand what it means. I only know that the program don't run.
It