Hi Antti,
Many thanks for the suggestions. You're right, I was mixing up the way memory settings work for MPI and OpenMPI.
However, unfortunately this does not seem to be the problem - when reran the MPI calculation with maxcore set to 4000, the job failed in the same way.
I also checked the stacksize in the way recommended for MPI jobs "ssh <hostname> ulimit -a" which showed that stack size, max memory size, file size and virtual memory size were all set to unlimited.
Finally, I also tried the SMP OpenMPI RICC2 version by setting PARA_ARCH=SMP, and setting maxcore to 16000. This also failed in the same way. "error in gradient step".
Any more ideas/suggestions would be much appreciated! In the mean time, I'll see if a serial run will work.
Many thanks,
Mike