If it does not work on 1 out of 200 machines, and if the machines are otherwise identical in terms of OS and other installed software, then it might just be that the install file is corrupt or damaged. I know it might sound obvious, but have you tried re-installing from scratch on those machines where the problem occurs?
Yes, I tried several times. I made an EXE version which does not suppress the DOS shell...as I wanted to see what is going on in the "backstage". Actually, I can leave with this problem, but it is I would like to understand. Anyway, thank you very much for your answers!