Hi,
I have six representative frames, in pdb format , of six clusters  evaluated with cpptraj of a trajectory .
For three representative frames  the command "coulombic protein" the surface is produced
without any problem whereas for the remaining three I receive errors similar to the following text:

coulombic protein
Using Amber 20 recommended default charges and atom types for standard residues
Assigning partial charges to residue CYM (net charge -1) with am1-bcc method
Running ANTECHAMBER command: /usr/lib/ucsf-chimerax/bin/amber20/bin/antechamber -ek qm_theory='AM1', -i /tmp/tmp76d1_frw/ante.in.mol2 -fi mol2 -o /tmp/tmp76d1_frw/ante.out.mol2 -fo mol2 -c bcc -nc -1 -j 5 -s 2 -dr n
(CYM)
(CYM) Welcome to antechamber 20.0: molecular input file processor.
(CYM)
(CYM) Info: Finished reading file (/tmp/tmp76d1_frw/ante.in.mol2); atoms read (22), bonds read (21).
(CYM) Info: Determining atomic numbers from atomic symbols which are case sensitive.
(CYM) Running: /usr/lib/ucsf-chimerax/bin/amber20/bin/bondtype -j part -i ANTECHAMBER_BOND_TYPE.AC0 -o ANTECHAMBER_BOND_TYPE.AC -f ac
(CYM)
(CYM)
(CYM) Running: /usr/lib/ucsf-chimerax/bin/amber20/bin/atomtype -i ANTECHAMBER_AC.AC0 -o ANTECHAMBER_AC.AC -p gaff
(CYM) Info: Total number of electrons: 94; net charge: -1
(CYM)
(CYM) Running: /usr/lib/ucsf-chimerax/bin/amber20/bin/sqm -O -i sqm.in -o sqm.out
(CYM)
(CYM) Running: /usr/lib/ucsf-chimerax/bin/amber20/bin/am1bcc -i ANTECHAMBER_AM1BCC_PRE.AC -o ANTECHAMBER_AM1BCC.AC -f ac -p /usr/lib/ucsf-chimerax/bin/amber20/dat/antechamber/BCCPARM.DAT -s 2 -j 1
(CYM)
(CYM) Running: /usr/lib/ucsf-chimerax/bin/amber20/bin/atomtype -f ac -p bcc -o ANTECHAMBER_AM1BCC.AC -i ANTECHAMBER_AM1BCC_PRE.AC
(CYM)
Charges for residue CYM determined
Assigning partial charges to residue CYM (net charge -1) with am1-bcc method
CYM: number of electrons (92) + formal charge (-1) is odd; cannot compute charges for radical species using AM1-BCC method

Any suggestions to solve this problem?

Thanks.
Saverio