It is just a warning, telling you that the automatic generation of dihedrals (based on the connectivity (the BONDs)) has not been performed for the three-membered ring. If this is OK for you, you don't have to do anything. If, for some reason, you want dihedral terms for the ring you can add them in the PRES.

Last edited by lennart; 06/30/19 03:34 PM.

Lennart Nilsson
Karolinska Institutet
Stockholm, Sweden