I have Thunderbird v140.3.1esr (64-bit) on Windows 10. I made a new calendar based on a google calendar. I have 2 google calendars so I am trying to import the second one from an .ics file exported from Google calendar, but each time I try it gives me an error message. An error occurred when writing to the calendar MyMotog! Please see below for more information. Modification_failed If you're seeing this message after snoozing or dismissing a reminder and this is for a calendar you do not want to add or edit events for, you can mark this calendar as read-only to avoid such experience in future. To do so, get to the calendar properties by right-clicking on this calendar in the list in the calendar or task view. It has installed itself as a second calendar in Thunderbird, but I've no idea why I can't import the one into the other?