I HOPE YOU KNOW, WHAT YOU ARE DOING
This is a warning resulting from ions being too close together in your structure. If you are working with highly compressed materials, it might make sense to ignore this warning. If not, it is certainly wise to check your POSCAR for mistakes.
Also check the RCORE value in the POTCAR file. You might run into serious issues if the pseudopotential cores start overlapping. Sometimes this can be fixed by using a POTCAR that has more valence electrons available.