trying to extract a seasonal subset of data

[Katherin Kullgren]

Hi,

I am trying to extract seasonal subsets of data from my dataset.
I  want DJF MAM JJA SON

So this is what I tried

'open anom.ctl'
'set gxout fwrite'

* This creates the DJF season from Dec1950/Feb1951 - Dec1999/Feb2000

'set fwrite djf.data'
imap = 12
pmap = 14
while (imap <= 600)
'set t ' imap pmap
'd anom'
imap = imap + 12
pmap = pmap + 14
endwhile

'disable fwrite'

This does not work. I am not sure the correct way  define the increments that I want.
I  want to have
set t 12 14
set t 24 26
 ..........
set t 603 605

I keep getting the error

Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
Data Request Warning:  Request beyond file limits
and so on

If someone could suggest a way that this would work.  I would appreciate it.
BTW- its monthly gridded data.

Thanks
Katherin