[ferret_users] Puzzling metafile error with Fprint

[Paul Young <Paul.J.Young@xxxxxxxx>]

Hi all,

I'm having a problem generating a postscript file using Fprint. I get  
the following error:

GKSM item 12121226 is undefined
ggetgksm()  163 Metafile item is invalid
greadgksm()  162 No item is left in GKS Metafile input

which I have not had any luck finding on these forums or via google.

Essentially, the problem seems to be related to my "shading" certain  
areas of a fill/ plot with plot/vs. Here's a sketch of what I am doing:

use my_data1.nc     !Time series of (e.g.) winter averages
use my_data2.nc

let variance1 = my_var1[d=1,t=@var]  !Standard deviation calculation
let sd1 = variance1^0.5

let delta = my_var2[d=2,t=@ave] - my_var1[d=1,t=@ave]
let signif = if abs(delta) gt sd1 then 1 else 0

set region/x=0:360/y=-90:-20              !Define SH region

set grid delta
go mp_stereographic_south 0 -40
fill/noaxes/nolab/lev=(-80)(-40,40,10)(80)/y=-90:-20/set delta,  
x_page, y_page
ppl title "1981to1986 - 1979to1980: Dec-May Avg"
ppl fill
go mp_land

plot/vs/over/sym=dot/nolab  x_page*signif, y_page*signif

-----
Removing the plot/vs removes the error, so I guess this is where  
things are going awry.

Btw, I tried using the polymark.jnl script to shade the data, but it  
just shaded a ring around the south pole - don't think I've got the  
command quite right:

go polymark poly/pal=black/over  xsequence(x_page), xsequence(y_page),  
xsequence(signif), circle, 0.2

As usual, thanks for any help,

Paul