I try to use ganttproject, an open source project management solution, with webdav. Opening the file from the webdav space works fine. Saving it (using Drupal user name and password) leads to errors, and I see the following in my Drupal logs:

Invalid argument supplied for foreach() in /var/www/apache2-myserver.com/modules/webdav/HTTP/WebDAV/Server.php on line 571

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1 query: SELECT p.perm FROM role r INNER JOIN permission p ON p.rid = r.rid WHERE r.rid IN () in /var/www/apache2-myserver.com/modules/user/user.module on line 502

array_keys() [<a href='function.array-keys'>function.array-keys</a>]: The first argument should be an array in /var/www/apache2-myserver.com/modules/user/user.module on line 502

implode() [<a href='function.implode'>function.implode</a>]: Bad arguments. in /var/www/apache2-myserver.com/includes/database.inc on line 241

array_fill() [<a href='function.array-fill'>function.array-fill</a>]: Number of elements must be positive in /var/www/apache2-myserver.com/includes/database.inc on line 241

This seams to be an authentication problem. Any help would be much appreciated.