Again, fwrite problem

[Mark Wang]

Hi all
I am trying to deal with the MM5v3 output data through GrADSv1.8SL11.
The MM5v3 programs are on Linux, and GrADS and Fortran77 are on DEC.
First, I can correctly use fwrite to convert MM5v3 data to GrADS output.
(Compare with MM5toGrADS and self-writing GrADS ctl files.)
But when I try to write a Fortran77 program to read the GrADS output,
I met a problem.

The xdef of self-writing ctl is:
xdef  41 linear 121.989  0.2027
ydef  32 linear  24.9028 0.2027

After execute GrADS, and open that ctl file.
The result of q dims is:
X is varying   Lon = 121.989 to 130.097   X = 1.00003 to 41.0001
Y is varying   Lat = 24.9028 to 31.1865   Y = 1.00001 to 32

Then I write a gs file,to fwrite variables without set any x or y dimension.
'open model_all.ctl'
'set fwrite model_all.bin'
tt=1
while(tt<=25)
 'set gxout fwrite';'set t 'tt
 level=1
 while(level<=20)
  'd h(z='level')'
 level=level+1
 endwhile
tt=tt+1
endwhile
'disable fwrite'

The message of fwrite is:
Wrote 1312 elements to grads.fwrite as Stream Little_Endian

The Fortran77 program is:
open(21,file='grads.fwrite',status='old',form='unformatted',recl=41*32)
do t=1,tt
 do k=1,L
  inum=k+(t-1)*L
  read(21,rec=inum) ((data(i,j,k),i=1,41),j=1,32)
 enddo
enddo

The program of Fortran77 is correct.
But when I execute the program, some kinds of errors happen:
forrtl: Not a typewriter
forrtl: severe(39): error during read, unit 21, file grads.fwrite

If the variables, times of fwrite data increase, the error become:
forrtl: Bad file number
forrtl: severe(39): error during read, unit 21, file grads.fwrite

All of these errors happen at the end of grads.fwrite file.
Could anyone help me solving this problem?
Thank you very much!

Mark