plot_swath problems

["Richard D. Slater" <rdslater@xxxxxxxxxxxxxxxxxxxx>]

I am trying to make some plots after the error_bars_demo script and am having 
some problems. I am using Ferret 5.22 running on intel-linux.

The plot in question compares the zonal mean results of 6 models. All models 
have been regridded to th same latitude grid. At each latitude I take the 
mean, minimum and maximum of the 6 models, ending up with three variables: 
mean, min and max, say. I want to plot the mean with an overlay of the range 
of model results. Something like (following the abovementioned script):

plot mean
go plot_swath poly/over/pal=gray/nolab min, max
plot/line=1 mean

However, when executing the go statement, I get an error message:

Command file, command group, or REPEAT execution aborted
 *** NOTE: error: data is not a line

This is very confusing, since I can successfully plot any of the lines 
individually:

plot mean
plot/nolabel/over min
plot/nolabel/over max

and this all works fine (but, of course, is not quite what I want :-) ).

Any ideas? I've tried simple things like:

go plot_swath poly/over/pal=gray/nolab mean-.2, mean+.2

and get the same error message.

Thanks for the help,

Rick Slater