After many hours of packetsniffing and debugging, it boils down to this:
- Windows Vista needs to be SP1 + Hotfix or SP2 to function 100%
- If you don't have SSL, you need to implement Digest authentication.
- If you have a self signed SSL certificate, forget it, it will fail. I had to use a trusted CA to finally get it working.
- In Windows 7 everything works out of the box.
The MAIN problem is that in Windows Vista and Windows 7, the Webdav implementation that comes with Windows is used. In earlier versions of Windows, the Webdav implementation that comes with Office is used, which is probably a lot more mature (Please correct me if I'm wrong).
Much kudos to this guy for writing up a good overview of the different DLL versions in different flavours of Windows. The list says Windows Vista without any service packs + the Hotfix will work, but for me I had to apply SP1 to get it to work.
For very interested folks, I have created a Webdav Compatibility Matrix you can check too.