aCalendar is not involved in calendar synchronization. The app is just an user interface to the Android calendar storage and does not save any calendar data itself.

If you have issues with synchronization and you have no shown error codes / messages please see: General Sync Issues / Sync of two devices

aCalendar is generally not involved in calendar synchronization, but displays error codes and error messages from the sync adapter, which handles synchronization between your chosen cloud service and Android.

For Google Tasks and MS Todo aCalendar does provide synchronization, however CalDAV Tasks configured via are synchronized by external sync adapters, e.g. davX5.

Android error messages

The Android system predefines several error messages for common problems:

  • already-in-progress, this can usually be ignored, it is shown when another sync request is issues while sync is still running.
  • authentication-error, this usually means, that the credentials are no longer valid, e.g. because a password was changed or permissions were removed. Usually the responsible app should ask for your credentials or consent again. Otherwise, try re-adding the account.
  • io-error, this can be any network-related problem (io stands for input/output). Check the internet connection and/or try later.
  • parse-error, a server message was in an unexpected format. Try again later, or if this doesn't help, re-add the account.
  • too-many-deletions, some sync adapters limit the number of items to be deleted at once to avoid accidental mass-deletion of your data. The sync adapter should prompt you to confirm or undo the deletions. If you are not prompted for this, check if the sync adapter app has notification permissions.
  • internal-error, this can be any internal problem within the sync adapter. Try again later, or if this doesn't help, re-add the account.  

Known sync-adapter-specific error codes

  • Sync Error 6 (Samsung Active Sync/Exchange Sync), some versions of the Samsung Active Sync adapter fail to edit/create any event with an Outlook category set. You must remove any Outlook category before editing the event. Removing the category after the sync error shows does not fix the event's sync status.