This may happen when uploading file with a name that already exists via WebDAV:
PHP Fatal error: Undefined class constant 'ERROR_FORBIDDEN' in /usr/share/iRony/lib/Kolab/DAV/Node.php on line 209
[31-Jan-2017 17:12:45 UTC] PHP Stack trace:
[31-Jan-2017 17:12:45 UTC] PHP 1. {main}() /usr/share/iRony/public_html/index.php:0
[31-Jan-2017 17:12:45 UTC] PHP 2. Sabre\DAV\Server->exec() /usr/share/iRony/public_html/index.php:194
[31-Jan-2017 17:12:45 UTC] PHP 3. Sabre\DAV\Server->invokeMethod() /usr/share/php/Sabre/DAV/Server.php:254
[31-Jan-2017 17:12:45 UTC] PHP 4. Sabre\Event\EventEmitter->emit() /usr/share/php/Sabre/DAV/Server.php:469
[31-Jan-2017 17:12:45 UTC] PHP 5. call_user_func_array:{/usr/share/php/Sabre/Event/EventEmitterTrait.php:105}() /usr/share/php/Sabre/Event/EventEmit
terTrait.php:105
[31-Jan-2017 17:12:45 UTC] PHP 6. Sabre\DAV\Browser\Plugin->httpPOST() /usr/share/php/Sabre/Event/EventEmitterTrait.php:105
[31-Jan-2017 17:12:45 UTC] PHP 7. Sabre\DAV\Server->createFile() /usr/share/php/Sabre/DAV/Browser/Plugin.php:157
[31-Jan-2017 17:12:45 UTC] PHP 8. Kolab\DAV\Collection->createFile() /usr/share/php/Sabre/DAV/Server.php:1053
[31-Jan-2017 17:12:45 UTC] PHP 9. Kolab\DAV\Node->throw_exception() /usr/share/iRony/lib/Kolab/DAV/Collection.php:195