[gradsusr] Superimposing data from different dat files

[Salvador Salazar]

Hi guys,

I'm having trouble superimposing two graphs from different dat files.
One file was custom made by a colleague which has temp from Feb 2 to
Feb 7 among other variables. The second dat file comes right out of a
WRF simulation, which was then sent through ARWpost for Feb 1 to Feb
5. When I open the ctl files individually on Grads, I can plot the
graphs of the respective data. But, when I open both ctl files in a
single Grads session, only the first file will be able to plot
anything. Right now, I'm only interested in plotting temperature in
Celsius from Feb 2 to Feb 5 over a specific station. (Variable 'tc'
from the ARWpost ctl, and variable 'temp' from my colleagues data.)
Here's the error message:

Data Request Error: Invalid grid coordinates
  World coordinates convert to non-integer  grid coordinates
    Variable = tc.2  Dimension = 0
  Error ocurred at column 1
DISPLAY error:  Invalid expression
  Expression = tc.2

Thoughts?

Any help would be greatly appreciated!