Saisie d'écran (screen catching)

Hello,
my backup protocol is "1 complete backup every 5 incremental backups."
I would like to catch the screen at every backup.
It works fine approximatively at 50%.
50% times, it'OK, 50% times, it says "la saisie d'écran n'est pas disponible pour cette version" (screen catching is not possible for this version).
Has somebody an idea ?
(Naturally, the flag "screen catching" is OK, naturally I tried to uninstall / reinstall)

Thank you
Philippe Bullot