Please upload and/or provide the full log or report of the error. Looking foorward to help you as I can...!

One or more worked in mine-

1. Add polar hydrogen atoms in PyMol before making topology file in gromacs

2. Open your pdb file in swiss pdb viewer and fix it (not sure).

3. use -ignh at the last of the command line with pdb2gmx

gmx pdb2gmx -f 2C65_clean.pdb -o 2C65_processed.gro -water spce -ignh

if the error persists, remove the residue Asn3 from the protein. Removing a single residue from the terminal, will not be a problem.