Group Protein_UNK referenced in the .mdp file was not found in the index file

[Tanvir]

GROMACS version:21
Fatal error:
Group Protein_UNK referenced in the .mdp file was not found in the index file.
Group names must match either [moleculetype] names or custom index group
names, in which case you must supply an index file to the ‘-n’ option
of grompp.

As the error suggest Protein_UNK is not found in the index file. But surely i have generated Protein_UNK . Anyone please help to solve this error .

index file

[jalemkul]

The existence of an index file is insufficient; did you do this:

@Tanvir

in which case you must supply an index file to the ‘-n’ option
of grompp.

[Tanvir]

Thanks . Now it works just fine … Thanks a lot again .