Neutral sparking in panel
The neutral wire is sparking because it is loose and carries a load.  Technically this is referred to as a non-linear load, or a unbalanced load. 

Most folks just refer to it as the return load, or neutral load. 

Solution

A qualified technician should tighten the loose screw and give a slight tug on the wire to carefully make sure it is secured and not damaged from the arching.  Also while the panel cover is open, the qualified tech should make sure all the other terminal connections are secured and not loose.

I personally would not recommend this as DIY job.