The button is disabled if the calendar doesn't support custom alarm sounds for events.
But the alarm will sound in my PC through Rainlendar. Google hasn't sounds. Google is the calendar server, the sounds are part of client program!
In my cell phone the Google alarms has its own sounds, this sounds are configurable in the client, never in the server. All Google clients work of this form.
Until now, it was permitted and it worked properly. Why now not?
What sound uses Rainlendar for this events? Nothing?