Reading Ascii data file

["Mr. P.Chitti Babu" <pcbabu@xxxxxxxxxxxxxxxxxxxxxx>]

I am new to Ferret. I am using ferret 4.91 version on sgi. I am placing 
problem in reading a missing value in a ascii data file.
I am getting this message at Ferret command prompt.

yes? DEFINE AXIS/X=65E:100E:0.25/UNIT=DEGREE LONGITUDE
yes? DEFINE AXIS/Y=2N:25.25N:0.25/UNIT=DEGREE LATITUDE
yes? DEFINE GRID/X=LONGITUDE/Y=LATITUDE gsurge
yes? FILE/GRID=gsurge/BAD=-999/VAR="PS" pksur.dat
**ERROR: unknown command qualifier: BAD=-999
any help?
Thanks in advance

chittibabu.P 

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P.Chittibabu                          e-mail address pcbabu@cas.iitd.ernet.in
                                                     pcb1960@hotmail.com
Centre for Atmospheric Sciences       tel. 91 -11-686 1977 extn: 6052 
Indian Institute of Technology        fax  91-11-6862037
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