need helps

[Jim Bao]

Dear GrADS Users,
    I want to use data from Northern America Regional Reanalysis
(NARR), and while I run GrADS, I don't know why I couldn't open it.
For example,  ga> sdfopen air.197901.nc
Scanning self-describing file:  air.197901.nc
SDF file has no discernable X coordinate.
  (under v1.8SL11 32-bit little-endian readline sdf/xdf netcdf lats printim).

     Whether is v1.8 not supporting or other questions, please give helps.

     Best regards

       Jim