file not present or wrong filename - when using >=4 procs

Hi,

I have an intel i7-4770 cpu.

Running my CFD simulation code using 1 - 3procs works well. However, when using >=4 procs, I almost always get 2 lines of the error:

file not present or wrong filename.

Occasionally, I can get the code working, but it's like 1 out of 20 tries, although it can be quite random.

I guess it has to do with some file opening:

do ijk=0,num_procs-1

    call MPI_Barrier(MPI_COMM_WORLD,ierr)

    if (ijk==myid) then
        
        open (unit = 44 , FILE = "ibm3d_input.txt" , status = "old", iostat = openstatus(4))

        if (openstatus(4) > 0) then

            print *, "file not present or wrong filename."

            stop

        end if

        read (44,nml = solver_input)

...

It happens also when I simply use:

open (unit = 44 , FILE = "ibm3d_input.txt" , status = "old", iostat = openstatus(4))

if (openstatus(4) > 0) then

print *, "file not present or wrong filename."

on all procs.

Do I have to use mpi commands like MPI_FILE_OPEN for file opening?

Or how do I avoid this problem?

Thanks!