Disable your antivirus and re-patch. You can re-enable your antivirus afterwards.
This error presents itself when you're missing the container.zD file. Use the installer again, and hit "Repair Game" in the installer options and it should fix the issue.
Uninstall Eclipse FlyFF from your computer, go back to the download page, choose another mirror and run both the installer and patcher as administrator.
Close all of your Neuz instances and re-patch. If the patch does not patch any new file, delete version.xml & Neuz.exe from your Eclipse FlyFF folder, and try again.
The game saves the position of the windows on the last client you close, so make sure you move them on this one. If this does not work, it means Eclipse FlyFF does not have permissions to write in the directory it is in. To fix this, either start the patcher as administrator, or move the directory somewhere it has writing permissions in.