Something went wrong with calendar sync? This page explains what the error messages mean – and what you can do about them.

1

Important: aCalendar does not sync

Before troubleshooting, it helps to understand how sync works:

aCalendar does not synchronize your calendars itself. It only displays what Android stores. The actual sync between your phone and the cloud (e.g. Google) is handled by Android and your account’s sync adapter – not by aCalendar.

aCalendar does however show you the error messages that come from that sync adapter, so you know something went wrong.

No error codes shown but sync still not working?
See: General Sync Issues / Sync of two devices

Special cases where aCalendar does handle sync itself:
Google Tasks and Microsoft To Do are synced directly by aCalendar. CalDAV tasks configured via tasks.org are synced by an external adapter such as DAVx5.

2

Android error messages explained

Android uses standard error messages for common sync problems. Here is what they mean and what to do:

already-in-progress

What it means: A sync was requested while another sync was still running.
What to do: You can usually ignore this. Wait a moment and try again.

authentication-error

What it means: Your login credentials are no longer valid – for example because you changed your password or revoked app permissions.
What to do: The responsible app should ask you to log in again. If it doesn’t, try removing and re-adding the account.

io-error

What it means: A network problem occurred (io = input/output, i.e. data transfer).
What to do: Check your internet connection and try again later.

parse-error

What it means: The server sent a response that Android couldn’t understand.
What to do: Try again later. If the problem persists, try removing and re-adding the account.

too-many-deletions

What it means: The sync adapter detected a large number of deletions and paused to protect your data from accidental mass-deletion.
What to do: You should receive a prompt asking you to confirm or undo the deletions. If you don’t see a prompt, check whether the responsible app has notification permissions enabled.

internal-error

What it means: An internal problem occurred within the sync adapter.
What to do: Try again later. If it keeps happening, try removing and re-adding the account.

3

Specific error codes

Some error codes are specific to certain apps or account types:

Sync Error 6 Samsung / Exchange

What it means: Some versions of the Samsung ActiveSync adapter cannot edit or create events that have an Outlook category assigned.
What to do: Remove the Outlook category from the event before editing it. Note: removing the category after the sync error appears will not fix the event’s sync status.