[gmx-users] Error using pdb2gmx tool

[ankit agrawal]

hi,
I was simulating A cadherin molecule (PDB ID: 4APX). I removed all the
water molecule from molecule then ran the following command.

pdb2gmx -f 4APX.pdb -water tip3p

then I chose force field : CHARMM27 (with CMAP) after that it should create
3 types of files  (.gro, .itp, .top) but it is not generating the .gro file
and showing an error.
"Fatal error: Residue 'CA' not found in residue topology database".

Please help me to solve this error.