I have done simulation of protein-ligand complexes with gromacs version 2020.4. For mmpbsa calculations i installed g_mmpbsa with gromacs version 5.1.4 and I recreated tpr file with gromacs version 5.1.4.

After ruunning g_mmpbsa -f md_100_center.xtc -s mmgbsa.tpr -n index_mmpbsa.ndx -pdie 2 -decomp I am getting memory allocation error.

Not enough memory. Failed to calloc -1082130432 elements of size 4 for grps[j].nm_ind

(called from file /home/rajendra/software/gromacs_source/gromacs-5.0.7/src/gromacs/fileio/tpxio.c, line 2510).