[gmx-users] REMD - subsystems not compatible

[Per Larsson]

Hi gmx-users, 

I am trying to start a replica exchange simulation of a model peptide in water, but can’t get it to run properly. 
I have limited experience with REMD, so I thought I’d ask here for all the rookie mistakes it is possible to do.
I have also seen the earlier discussions about the error message, but those seemed to be related to restarts and/or continuations, rather than not being able to run at all. 

My gromacs version is 2016 (for compatibility reasons), and the exact error message I get is this:

-------------------------------------------------------
Program:     gmx mdrun, version 2016.5
Source file: src/gromacs/mdlib/main.cpp (line 115)
MPI rank:    32 (out of 62)

Fatal error:
The 62 subsystems are not compatible

I followed Marks tutorial on the gromacs website and have a small bash-script that loops over all desired temperatures, run equilibration etc. 
I then start the simulation like this:

$MPIRUN $GMX mdrun $ntmpi -ntomp $ntomp -deffnm sim -replex 500 -multidir ~pfs/ferring/gnrh_aa/dipep_remd/sim* 

What could be the source of this incompatibility?

Many thanks
/Per