Error deleting last empty folder

I have nothing left in my owncloud except one empty folder. I can not get it deleted wether from the web interface or the iphone app. It keeps giving an error. I also deleted all deleted files/folders from the restore area. The error below mentions a lock issue. How do I correct this?

Server configuration
Operating system: Ubuntu16
Web server:Apache
PHP version:
ownCloud version (see ownCloud admin page):9.1.3
Updated from an older ownCloud or fresh install: from 9.1.0
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):
external hdd
ownCloud log (data/owncloud.log)

Please paste possible errors in the following code block, see for more info

Exception: {"Message":"HTTP\/1.1 423 \"FOLD\" is locked","Exception":"OCA\\DAV\\Connector\\Sabre\\Exception\\FileLocked","Code":0,"Trace":"#0

Integrity status for oC9+

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