Problem reading files when more than 1 is opened

[Mark Schuster]

Hello

I am using windows 98 platform for grads, and I am having trouble.  I am
trying to calculate precipitable water so I need to know the surface
pressure and specific humidity.  I have the two files shum.nc and
pres.nc..both of which are on the same grid, but shum.nc has 8 levels in
the vertical.

When I open up just one of the files, I can read the data in them, but
suppose i open up shum.nc, and then open up pres.nc as file 2, i have a
problem.  Suppose after opening them both up, I type

d pres

I get an error message saying that the program has performed an illegal
operation and will be shut down.  Somehow, opening up shum.nc first is
doing something....I suspect it has something to do with the differing
levels in the vertical of the two files since pres.nc is just surface
pressure so it has no levels in the vertical.

But suppose i open two files where both have the same vertical levels, such
as uwnd and vwnd...then i can read them both just fine when both are
opened, so as I said, I believe it has to do with the differing vertical
levels.

However, I would like to use the vint function to calculate the water
content over the grid, so I type

set t 1
set lat 50 70
set lon 230 250
d vint(pres.2,shum,350)

and in my opinion, that should work (and I should get a contour plot of
precipitable water), but I keep getting all these error messages.  Can
anyone tell me what I am doing wrong?

Thanks a lot

Mark