vector plotting

[Muyin Wang <muyin@xxxxxxxxxxxxx>]

Dear Ferreters:
  I have this strange problem: I tried to plot vector field overlay on top of
temperature (shaded). There are 12 panels on each page. The figure looks fine on
the screen, but I coud not ask ferret to convert it to postscript. When I tried 

sp (Fprint -o fig1.ps -p landscape metafile.plt)
I got the following message:
 greadgksm()  165 Content of item data record is invalid for the specified item
type

However if I run the save scrip without vectors overlay, then the everything
works fine. Does anyone know what does this error message mean?

Here is just one sample of what I am using for the plottings:

ppl axlen 3.5 3.5
set region/z=1000
shade/set/noaxis/nolab/nokey/levels=(-7,8,1) $5,x_page,y_page
ppl xlab 1000mb
ppl shade
vector/set/color=1/nolab/noaxis/length=$2 $3,$4,x_page,y_page
ppl veckey/nouser,2.9,0.1,,10.0
ppl vector/over,4,2,,
go mp_graticule 0 360 90 40 90 20 1
!go mp_land 1 over1lay

where $2=10, $3,$4,and $5 are the variable names to be passed in when the script
is called


Any suggestions?
Thanks a lot!

Wish you all have a happy holiday!
Muyin