pyMPI error on mpi.barrier()

[Dina Ali]

Hello there

I am trying to paralleize GA code using pyMPI. part of the code and and the
error message is as below.
i write the new positions in a file by root (which is mpi.rank = 0) then
other processes are suppose to wait
until the written in the file finishes to start evaluating the objective.
the problem arises in the barrier method...
any ideas on how to do this would be very much appreciated..

Thanks very much
Dina

for i in xrange(max_iter):
            if (mpi.rank == 0):
                update_positions()
                save_pso_pops_iter()

            mpi.barrier()  <----------------------------error is here
            evaluate_objective()
            mpi.barrier()

error message:
    mpi.barrier()
mpi.MPIError: MPI_Error_string: invalid communicator: Input/output error
(pyMPI_comm_io.c:367)
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