Strange error message when loading FS9

hii had to install my system from scratch. this week installed a vanilla version of FS9.1. After having installed now several add-ons, suddenly a message popped up when loading FS9. there is a dialog coming up and in the window title is says "unknown name". i can click on OK and FS9 loads normal. i can play normal. there is nothing that is not working as it should. the last add-on i installed before the message came up was FS Flightdeck 4.does anyone have an idea what this could be or how i could debug?thanks for helpcheersMartin