Ions.tpr file

GROMACS version:
GROMACS modification: Yes/No
I work on ligand receptor simulation by gromacs.
i did step by step stages tutorial complex ligand protein simulation with charm forcefield 36. Ligand str file constructed by website CGENFf. In step construct ions.tpr file i received error
ERROR 1 [file ligand.itp, line 540]:
No default Proper Dih. types.
How can i solve it?

You likely didn’t #include the .prm file that the ligand requires, which contains the new bonded parameters used by the ligand.