Hi guys
First a special "thanks" to Samuel for your advice and workaround
As I am the admin of the Web Server IIS, I check in my php.ini and with an echo get_temp_dir(); whic directory was used by WP before adding the workaround line inwp-config.
So I tried to add Full control permission to my App pool identity over this directory (the one in php.ini) and indeed, it works well ;-)
Do you see any danger in working around the way I just explained instead of addingline to wp-config.php ?
Thank you ...