>>Can anybody explain me why there seems to be a problem with random numbers and a delay?

Certainly seems odd...

Re the randomizing code: if I read it correctly, starting thisform.nTot at 75 then decrementing after each hit means 75 can only ever appear first in the sequence since thisform.nTot then decrements to 74; and 74 can only appear first or second, etc etc. This means you can anticipate a preponderance of lower duplicates that can often follow very similar sequence as nTot decrements towards 1, while higher numbers are infrequent and always earlier than (77-n) in the sequence if they do appear.

To randomize all numbers in a series, I've seen efforts like this that scatter high and low values and eliminate duplicate returns:

=rand(-1)
declare laNumber(75)
for licounter=1 to 75
   laNumber(m.licounter)=m.licounter
endfor
for licounter=1 to 75
   liRandom=int(rand()*(76-m.licounter))+1
  ? lanumber(m.lirandom)
  adel(lanumber,m.liRandom)
  *WAIT timeout 8
ENDFOR