This seems to be the same problem as https://forums.bitfire.at/topic/1100/v1-0-9-http-1-1-415-unsupported-media-type
Please use DAVdroid 0.9.0.1.
I use the latest DAVDroid to synchronise my contacts and calendars with DAViCal server (on Ubuntu 12.04) and Thunderbird Lightning 3.3.1.
I wanted to attend this event: https://www.facebook.com/events/390872961070320/?ref_dashboard_filter=past I exported this event in ICS file and added it to my calendar via Thunderbird. When later I tried to synchronise DAVDroid, it complained about failed syncronisation. After removal of this event the issue disappeared. Another test confirmed it is exactly this even that causes sync to fail.
When I open the ICS file in the text editor it looks good to me. I assume there is a problem with DAVDroid parser.
Thanks for your report.
E/davdroid.DavSyncAdapter(16580): Caused by: android.os.TransactionTooLargeException
The number of items in this VCALENDAR is too big for the transaction. Adding every event is wrapped in a transaction (already one transaction per event).
This is a duplicate of #274.