Gravity effect of a layer

Hello,
 
I have a grid of sediment thickness data and would like to correct the gravity data for this.
 
I have looked at grdgravmag3d and this should be fine, but when I tried this route it gets stuck:
 
grdgravmag3d -C2000 -GSeds_thick_clipped_grav.grd -V -fg Sediment_thickness_clipped.grd -I1m -Z
grdgravmag3d: Grid dimensions are nx = 2581, ny = 1441
grdgravmag3d: Allocates memory and read data file
Line = 0         of = 1441  <----- hangs here!
 
What I am looking to do is a sediment corrected Bouguer.
 
Any pointers would be useful.
 
Thanks
Lester
 
 
 		 	   		  
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