I installed the application and as the instruction I pressed Ok button. But the screen immediately closes as I press the button. What's causing the error?
This error is a bug in the f.lux application.
Drag the f.lux notification window out of the way, fill in your longitude and latitude or zipcode on the f.lux preferences screen, and click the Close button on the preferences screen. After that click the OK button to close the f.lux notification window.
If that doesn't work try closing the notification window by clicking on the X.
If that doesn't work uninstall f.lux, reinstall it, and try again. Be careful filling in the preferences screen. If you make a mistake, f.lux won't let you change it without uninstalling and reinstalling the application.