How to fix a short circuit?
Make sure you turn on the design rule checks in KiCad, and that all of the clearances are set as your fabricator recommends.  

There'll be a minimum distance between vias, and there'll be a minimum distance between vias and traces.  There's more than that, but those are the two that probably bit you this time around.

What has probably happened is that the vias (or the vias and some trace) were placed closer together than your fabricator can cleanly etch the traces and drill and plate the vias.  

KiCad doesn't show a short because it shows you what an ideally fabricated board would look like.



Whoops.  Re-read the question.  Shorted to ground.  Same problem, different place, same solution.

As an example, here are the recommended clearances and trace widths for Eurocircuits (where I have my boards made.)


  4 Layer Base copper outer 18µ inner 35µ
  
  
  Min Track with OL 0.150mm
  Min Clearance OL 0.150mm
  Min Track with IL 0.150mm
  Min Clearance IL 0.150mm
  Min via Drill Diameter 0.35mm (Tool size)
  Min via Pad Diameter OL 0.600mm
  Min via Pad Diameter IL 0.600mm
  


Check what your fabricator recommends, and set KiCad to use those values - then make sure you've turned on the design rules check.  That's the bug shaped icon on the PCBNEW toolbar.