hey Cupcake have you already tried to open the Fiesta folder and delete the file FiestaOnline.new?
Hey Enbi, thank you for your suggestion! I've resolved my issue thanks to Akher via Discord since he posted there how to solve the laucher problem and it worked for me! I forgot to update the thread here - but thanks for your kind support!
As for Nekkame's issue, by reading the Discord (question_and_answers and general_issues channels) it seems like people who had similar issues as yours just end up reinstalling the game and had it fixed, if nothing works I guess that's the ultimate option left.
(When it comes to launch the game I've always been told to remember to run it ad admin, not sure if you have done that already or not!)