A solution
Hi,
Finaly found a solution:
* Logged in as Admin
* Clicked on Start, All programs (translated from French)
* Clicked on Windows update
* After search, application said 2 updates, related to Net Framework 4, were downloaded but not installed
* Deactivated the antivirus
* Clicked on Install
Installation went ok, and no more prompt for installation on shutdown.
Bye.