The conventional MFCC scheme yields rather crude approximations to the protein-ligand interaction energies in most cases. The largest errors of 332 kJ/mol (for ε = 4) and 246 kJ/mol (for ε = 79.39) are found for 2PK4 (with the zwitterionic ligand). For the cases with multiply charged ligands, the MFCC errors amount to 89 kJ/mol and 153 kJ/mol for 1AAL and 1A6F, respectively. For the test cases in which the ligand carries a single negativ charge, we find MFCC errors between 4.3 kJ/mol and 182.4 kJ/mol. In general, the errors are lower in the calculations using ε = 79.39. The very low error of only 4.3 kJ/mol in the calculations for 1TOW using ε = 79.39 seems to be coincidental, as a rather large error of 106 kJ/mol is obtained for the same system when using ε = 4.