Operation Canceled and and slow to sync file in client

Hello all,

Please help me, our server using Ubuntu 14.04 and OC 8.2.11. Now our server have one trouble about synchronize client with the server. Error Message like this

operation canceled.
XXXXXXXX/remote.php/webdav:service unavailable.

Hello, OC 8.2.11 is out of life. Update to 10.0.3 . several sync problem are solved with this update.