January 6th, 2020 Update:
As of today, I will no longer be updating or maintaining the game files, nor will I be checking in on the forums very often, soon to be at all. It's been fun helping you all out over the last several years, but it's time for me to retire because I no longer play Aion nor do I plan on returning to Aion.
Thank you, all, for all the help, service, support, and love over the last ten years.
If you're getting this error while downloading the game, send a ticket to Support here https://support.aiononline.com/.
Old potential fix was getting the broken folder/file directly from another player, but I'm not going to pay to maintain my collection of Aion files any longer, since I can't update them, anyway.