[gmx-users] pdb2gmx error

[Gadzikano Munyuki]

Hi, i am new to gromacs want to do dynamics on a cyclic polypeptide. The peptide contains a residue that is not standard.I however have included this residue in the ffaoplsaa.rtp file as well as the aminoacids.dat file. When i run  pdb2gmx its giving me a fatal error and its saying the residue is not in the residue topology  database.
What could be the problem?
Thanks