Error 80004005 when accepting an invite

[aik_au]

TB60, fedora27, Google calendar at https://www.google.com/calendar/dav/<my ... re>/events, read/write, works fine. I have an entry and I received an update, TB recognized it as an update (crossed out old time) but clicking on accept/decline/... produces the same window with "Processing message failed. Status: 80004005" which does not really explain what happened.

Write access works - I can add events to my googlecal. It is this update which is problematic.

How do I apply an update? I have a suspicion it is trying to update a calendar with no write access as I have 6 of them and all others are googlecal too but ics'.

[aik_au]

I even deleted the original event but TB keeps saying "This message contains an update to an existing event.". How do I tell where it found it?