[gradsusr] problem with an extract script

[Ismaila Diallo]

Dear Grads User's

i've daily data for a big region. Now i try to extract since this file the data 
available for an area and this extract data must be only the data average of 4 
months (june july august and september. so that i perform this script: 


'reinit'
'sdfopen /home/lpaosf/RT.1996-2007_DAY.AVG.NC'
t=518
tmax=3926
'set fwrite test.dat'
'set gxout fwrite'
while (t<=3926)
   'set t 't
   'define jun=ave(rt,t=t+0,t='t+30')'
   'set t 't+30
   'define jul=ave(rt,t=t+0,t='t+31')'
   'set t 't+61
   'define aug=ave(rt,t=t+0,t='t+31')'
   'set t 't+92
   'define sep=ave(rt,t=t+0,t='t=t+30')'
   'define jjas=(jun+jul+aug+sep)/4'
   'define aa=ave(jjas,lon='-8.5',lon='8.5')'
   'define bb=ave(aa,lat='10',lat='16')'
   'd bb'
  t=t+365
endwhile
'disable fwrite'

but with this script i get some errors and i don't understand what's wrong in my 
script.
so could someone help me to resolve this difficult.
Believe in your great Help.
Sincerely
Ismaila