owncloud complains about locked files

put ownCloud in maintenance mode: 
edit /var/www/owncloud/config/config.php and change this line:

'maintenance' => false,

to

'maintenance' => true, 

bash# cd /var/www/owncloud/data

bash# sqlite3 owncloud.db

sqlite> DELETE FROM oc_file_locks WHERE 1;

sqlite> exit;

then  

edit /var/www/owncloud/config/config.php and change this line:

'maintenance' => true,

to

'maintenance' => false, 

https://central.owncloud.org/t/file-is-locked-how-to-unlock/985