The beta edition of Calendar Sync for Android is currently available for download only on the Android Market. Find it by running the Market app on your phone and searching for "caldav". Note that Google sometimes restrict the applications that are available in different countries or on different models of mobile device.

Protected apps don't appear sometimes on the market if your new phone OS/Firmware hasn't been registered by Google. How long this takes to happen (and so how long until you can see and download the app) is out of our control. The app is not available on newer versions of Android (see below).

Development of CalendarSync for Android is frozen (and hence not tested on new Android versions) while a new replacement app supporting Android 2.2+ is being developed. The new app will be available in the coming weeks.

The current version of Calendar Sync for Android requires a URL to a single calendar events collection, not the top-level server URL. This means the name or id of an individual calendar should appear somewhere in your URL, or you may get an error connecting.

In general, follow your CalDAV server's guide documentation as if using Mozilla Lightning/Sunbird. Specific examples for some CalDAV servers are given below.

Follow the Yahoo sync guide for Mozilla Lightning/Sunbird.

Your calendar URL should be like this:

https://caldav.calendar.yahoo.com/dav/username/Calendar/calendar_name

Follow the Google sync guide for Mozilla Sunbird.

Your calendar URL should be like this:

https://www.google.com/calendar/dav/calendar_id/events

Note: CalDAV on Google Calendar is a Google Labs feature. Synchronsing using the Google Sync feature provided as part of Android OS is recommended instead.

Follow the Zimbra wiki guide for Lightning.

Your calendar URL should be something like this:

https://server_name/dav/username/calendar_name

Follow the Scalix CalDAV connection guide.

Your calendar URL should be like this:

http://server_name/api/dav/Calendars/Users/user@domain/calendar_name

Note: The URL format for your Scalix installation may differ from the default Scalix URL above. Please check with your Scalix server administrator.

Your calendar URL should be like this:

https://<server:port>/calendars/__uids__/<XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX>/<calendar_name>/

Note: The last / in the url seems to be important for Darwin. If you omit it, you may get a response error from the server.

The Android OS does not support self-certified server certificates directly, and will reject such HTTPS connections with the message "Not trusted server certificate".

As of version 0.9.2.0, you can accept these certs by checking the option "Accept SSL Certificates from untrusted sources" in the advanced connection settings. Note: enabling this option could expose you to man-in-the-middle attack. You must ensure for yourself that you can trust this server/certificate.

You will get this error if you are connecting to a CalDAV server via HTTPS and the server's SSL certificate has not been signed by one of the common Certificate Authorities supported by Android (e.g. Verisign, Thawte, etc).

This is especially a problem for servers that use self-signed certificates (such as a server identified by an IP address, rather than a registered DNS domain name).

As of version 0.9.2.0, you can solve this by checking the option "Accept SSL Certificates from untrusted sources" in the advanced connection settings.

If you are still getting the error after that, it may mean that the server certificate is invalid (e.g. it has expired and should be renewed).

The login username and password combination you entered is not recognized by your CalDAV server. Check the credentials you are using and how you have entered them. Note that the Android text entry may have capitalized the first letter of your login username or password. Most CalDAV servers are case-sensitive.

"Method Not Allowed" frequently (but not always) is caused by using an incorrect CalDAV URL for accessing your server's calendar. It could also mean your server doesn't support CalDAV. Check the connections section above for the format of the URL for your server. Verify that the URL is correct and CalDAV functioning by trying it in Mozilla Lightning or similar.

If you are setting up a calendar to synchronize for the first time, "Forbidden" frequently (but not always) means Calendar Sync cannot query for calendar events at that given URL. This usually means that the URL you entered is valid, but is not the correct URL to your calendar events collection. Check the connections section above for the correct format of the URL for your server. Verify that the URL is correct by trying it in Mozilla Lightning or similar.

If you are setting up a calendar to synchronize for the first time, "Invalid response from server" frequently (but not always) means Calendar Sync cannot query for calendar events at that given URL. This usually means that the URL you entered is valid, but is not the correct URL to your calendar events collection. Check the connections section above for the correct format of the URL for your server. Verify that the URL is correct by trying it in Mozilla Lightning or similar.

Fixes in some recent updates might break the synchronization record of some existing events. These errors will disappear over time as the synchronization time frame moves on. But you can clear these errors if you like by clearing the synchronization data.

Beware that this will remove all events from the calendar you synchronize into, and will only restore from the server only those in the synchronization time range. So please make sure you have synchronized all new events on the mobile calendar up to you CalDAV calendar first before taking the following steps:

* In the menu, select More, then select Delete Calendar Events.
* Check next to the CalDAV calendar you are getting the errors on and click the Delete button. This will remove all previously synchronized events from the remote CalDAV calendar on your device.
* On the main screen, click Synchronize Now, and the events within that time frame will be download to the selected device calendar without reporting the errors.

Unfortunately a technical limitation of the Android calendar means that this app can not create device calendars. If you wish to synchronize CalDAV events into a mobile calendar, but not have those events copied to another thrid-party server, then there are two possible workarounds.

Some device manufacturers have one standalone device calendar that is not synchronized to any remote server - you could select to synchronize CalDAV events into this calendar. It is also possible to synchronize more than one remote CalDAV calendar into this one device calendar.

If your device doesn't have this option, you could create a new remote calendar, synchronize it (which will create it on your phone), but then in the Android Sync settings, disable synchronization (or make it manual) for that calendar/account. Then select that calendar on your device to synchronize the CalDAV calendar into.

Synchronization will only download/upload events that fall within the selected time range, e.g. if you select 16 weeks - that will download events that are within 8 weeks either side of the current date & time on the mobile device.

There is also a known issue in that any events which are based on a repeating event which started outside the time range will not appear on the device calendar after synchronization. Work on addressing this problem for the next beta release is underway.