error message after running a "do" command in bootstrapping

edit

Hi all, I have got some problem when computing standard deviations for metafrontier parameters, which I have estimated previously, through bootstrapping. The error message starts after the do command and it says syntax error when generating variable. I appreciate your help. See the error message and the command that I have used below. Note that x*starb are previously estimated.

 |_sample 1 556
 |_matrix q = cowva
 |_matrix qstar = x*starb
 |_matrix e = q-qstar
 |_dim beta 5 1000
 |_set nodoecho
 |_set nooutput
 |_set ranfix
 |_do #=1, 1000
 |_gen newe = samp(e)*SQRT(N/(N-K))
 |_sample 1 556
 |_stat newe
 |_gen qnew = qstar+newe
 |_OLS qnew feed vet herd price / COEF=beta:4
 |_endo
                                    $
 ...ERROR..SYNTAX ERROR WHEN GENERATING VARIABLE
 |_matrix bstre = newe'
                      $
 ...ERROR..SYNTAX ERROR WHEN GENERATING VARIABLE
 |_matrix beta = beta'
 |_set output
 |_sample 1 1000
 |_stat bstre
 ...ERROR..VARIABLE bstre    DOES NOT EXIST.
 |_sample 1 1000
 |_stat beta
 |_stop

The command I have used is :

dim cowva 556
read (cow.txt) cowva / beg=1 end=556 list
sample 1 556
matrix q = cowva
matrix qstar = x*starb
matrix e = q-qstar
dim beta 5 1000
set nodoecho
set nooutput
set ranfix
do #=1, 1000
  gen newe = samp(e)*SQRT(N/(N-K))
  sample 1 556
  stat newe
  gen qnew = qstar+newe
  OLS qnew feed vet herd price / COEF=beta:4
endo
matrix bstre = newe'
matrix beta = beta'
set output
sample 1 1000
stat bstre
sample 1 1000
stat beta
stop

Thanks, Sirak