How to fix error in GROMACS "Invalid atom number 6920 in index file"

Hello, I'm trying to proceed with NVT equilibration using command gmx grompp -f nvt.mdp -c em.gro -r em.gro -p topol.top -n index.ndx -o nvt.tpr I get an error Invalid atom number 6920 in index...

01 January 1970 6,943 1 View