I was getting similar errors too.
I am using Mac OSX server 2.2.1 on Mountain Lion OSX 8.4
I followed the setup instructions on the Support page and successfully created and linked to the DAV folder.
I also wanted to set up other folders. I have different groups of users who need to keep their work private to their own group.
I found naming was very important. Names not starting with DAV won't work (they didn't for me, anyway).
I also found they must be created and set up from within the Server app (not via Finder). This way they are owned by the System Administrator.
I have now set up folders called DAV1, DAV2, DAV3, DAV4, etc. I then renamed them from within Server App (i.e. gave them a new (AFP) name like Colab1, Accounts, etc). So, when viewed on the server via the Finder they retain their original DAVx names, but when set up on their local Macs they set the path as https://<fqdn>/Colab1 or https://<fqdn>/Accounts etc.
Thanks to the contributors to this forum and others such as the Apple Support Communities and
http://httpd.apache.org and
http://hints.macworld.com/ They have been invaluable to me in setting up this Omnipresence server and enabling https. I hope my notes above help others.