[gmx-users] problem with NPT simulation

[Sundari]

Dear all,

I am doing a protein simulation. After NVT equilibration, I tried to do NPT
but everytime I got this error :-

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Program gmx grompp, VERSION 5.1.2
Source code file:
/build/gromacs-z6bPBg/gromacs-5.1.2/src/gromacs/gmxpreprocess/toppush.c,
line: 1806

Fatal error:
[ file posre.itp, line 5 ]:
Atom index (259) in position_restraints out of bounds (1-1).
This probably means that you have inserted topology section
"position_restraints"
in a part belonging to a different molecule than you intended to.
In that case move the "position_restraints" section to the right molecule.
For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors
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I generated posre.itp file using "gmx genrestr -f solv.gro -o " .

please, anyone help me to understand this grompp error.

Thanks in advance