Same here. Was about to do a flight with the 717 and I got an invalid credential error or something like that, then tried to open the Addon Manager and got this:
Activation is alive and well as per the website. Not sure what the hell went wrong within the last couple hours.
EDIT: Now I've got the initial screen saying "Thank you for purchasing the TFDi Design 717! To get started, simply click the download button below..." but obviously I've already got it installed. When I click download, I get "An error occured while downloading."
@turbofandude Is this the product of an update gone wrong or something?