I tried google before asking ;)
The only relevant answer was Hotkey Detective which you must pay to download :(
I haven't got any error message since i rebooted...
And as long as it's working ... :)
It can only have been a tray app or system service. Maybe my graphic card, even if i couldn't see any hotkey in the config panel.
Thanks for your answers ;) (and sorry for wrong section Mr Admin)