Hi Martin, I haven't run into your MPI_File_open issue (don't use it), but your code does fail for me too in the same way.
$> mpirun -np 1 -H localhost:1 ./fmpitest fmpitest:/usr/local/lib/libmpi.so.5.0: ./fmpitest : WARNING: symbol(mpi_fortran_statuses_ignore_) size mismatch, relink your program fmpitest:/usr/local/lib/libmpi.so.5.0: ./fmpitest : WARNING: symbol(mpi_fortran_status_ignore_) size mismatch, relink your program
The Fortran symbol error you see is common and I'm not sure of the cause. I did look into it at one point and decided all definitions were in fact identical, so it might be a weird compiler+linker issue. It's never been symptomatic beyond the warning so I ignore it. --John