If you are starting a calculation from the SYMBOL file, like for example an excited state calculation. You now need to include the XMOL.DAT file along with the rest of the files needed.
This is because the NBO driver that is now included in the NRLMOL code, needs access to the information stored there.
This only applies if you get the code from the Git repository.
If you don't have it, the go and "Git" it.