Here it is (only relevant parts, the whole script is checking various things before, not related to calibre)
Add books :
Code:
calibre-debug -s
calibredb --library-path %biblio% add -d %dest% 1>nul 2>&1
Export all data :
Code:
calibre-debug --export-all-calibre-data %destination% %calibre% > nul
Edit : I've just found out, if I remove the redirections ( 1>nul 2>&1), this message doesn't appear anymore.
Strange, I've been using this script for years.