IISExpress 7.5 and webdav

Reading the clear instructions from vikomall in this 2011 posting: http://forums.iis.net/t/1178397.aspx/1
, I thought installing/enabling webdav on IISExpress 7.5 would be a cinch, but apparently not: as soon as I made the modifications to applicationhost.config, the webserver stopped working. After some experimenting I found that the problem is:
<authoring enabled="true" />
right under the <webdav> element. As soon as put that in, the website stops working. Does anyone recognise this problem?
Additional info: i'm running IIS express 7.5 as a service under Windows XP and I use it for a public website (on port 80).