Google Apps for Work Calendar Sync

When I add my Google Apps for Work Account, I am receiving mails just fine but the calendar does not appear.
The error message I receive is:
[Google Calendar] Die Erkennung von Standard-Aufgaben brach mit folgender Fehlermeldung ab: Not Found

Translated to english:
[Google Calendar] The recognition of the standard-tasks stopped due to the following error message: Not Found

Thank you for your help.