Milioni88
That's a standard message saying you have a plugin installed, quite a few software products install their plugins for ETS2 / ATS, nothing to worry about. In the plugins folder (bin\win_x64\plugins sub directory of game directory), any .dll files in there will cause this message. If you don't want this message pop up again, you can check the plugins folder and see what plugins you have there, deleting those files will remove the message.
@Milioni88 why truckbook is seen as a plug-in, it is possible to prevent the game from seeing it as a plug-in