Error message in my “Create New Event” action

Hi all,
I have an error message question.
I have a Shortcut that has been functioning well till now.
It’s a simple calendar event creator that uses a “choose from list” to select the event type.
Then with “add new event” I populate the Apple Calendar with an event, for a specific calendar.
It allocates the event to one of 4 calendars, all iCal calendars.
Suddenly I get an error message on one of the calendar: ”this calendar is read only”.

There have been no changes to the rules of this calendar. I have checked all the settings for the calendar and cannot make it work.

If I enter the event directly into Apple calendar, using the same calendar that is generating the error message, it works fine.

Any ideas??

Thanks in advance