Unresolved atom types in fragment ILE M

Could anyone help me with this problem I met in QM/MM?  I used this command "ln -s /usr/local/NWChem/etc/default.nwchemrc $HOME/.nwchemrc". So I am pretty sure that my force field parameters directory was set up right! And the atom names, residue name in my PDB file match the names corresponding in the force field parameters. I don't know why I am still getting this error"Unresolved atom types in fragment ILE_M". Any guidance would be appreciated!