You need to make sure that your atoms are named correctly according to the topology database entries. There doesn’t seem to be a CG2 atom in residue 5 (THR) in your input file.
See if Residue mapped into topology database but atom name not found in file? - #10 by amei or Fatal error: Residue 1 named GLN of a molecule in the input file was mapped to an entry in the topol helps.