I've never had problems downloading Fiesta in the past, but after getting back on after years im running into alot of trouble. I've let the launcher patch everything and now trying to log in i get this messaged popped up. i've tried many solutions from reinstalling and restarting my computer. Just want to play with no problems!
use the repair tool to go back 2 or 3 versions and patch again to get a new Fiesta.bin file
Run as administrator first.
Also...if you just used Windows Uninstaller to remove the game...chances are some residual mess got left behind.
I suggest grabbing iObit Uninstaller and force uninstall everything and all registry keys and files that follow.
Also...using iObit's Advanced System Care to perk up your machine (if its not a custom build, or has a solid state) can prove...wonderful.
I've been using these products since they first came out and still do continuously.
Free and Paid versions of ASC, well worth the $ for the ultimate package also I might add.
Use the uninstaller I mentioned to obliterate Fiesta Online from your machine.
Try re-installing it on a removable media (I have a guide up here on the forums for a proper step-by-step means) and run it as an administrator.