Here's what I know:
- The problem seems to affect only some people.
- It doesn't affect all calendars (It looks that only the primary calendar causes the error. Please correct me if this is not the case)
- Authentication to Google's server works and also reading the list of calendars from the server
- Reading the events is what fails and the failure happens always with the same calendar
- Google tasks work fine
I don't know what triggered this error but it is something that Google has done to their service. The error just says "Internal error" without any additional information.
What I still would like to know is:
- How many events (i.e. more or less than 1000) do you have in the calendar that gives the error 500?
- If you set the "Import limit" setting e.g. to "Future only" does that get rid of the error?
- Are you able to read the xml or ical feeds from the Google's website? (click the XML or ICAL button for the private address in the calendar settings)
- Can you access the calendar via CalDAV? (Check the url from here: support.google.com/calendar/answer/99358?hl=en
- Does other calendars (e.g. Mozilla Lightning with the Google Calendar Provider) work?