We have a software that runs as hybrid MPI-OpenMP. We have tested it on RHEL 4, 5 and SUSE 10, 11. We have a client trying to run it onUbuntu10.04.2 LTS and it fails. The application is written in Fortran, compiled with Intel Fortran 11.1 and Intel MPI 4. We compile with command mpiifort and use -openmp flags. However on this Ubuntu system the only way we can get it running is if we don't use the -openmp flag and at linking stage use the flag -liomp5. What is the explanation for this? Thanks!