I was trying to create a WebDAV folder where I have UCM installed and Desk-Top-Integration suite installed too. I didn't install UCM on that environment, just I installed DIS and some other components, suddenly discovered I cannot create a WebDAV folder.
I tried to find the problem, but I didn't find any where I checked folder_g component and it's working, DIS installed correctly, CS is working, and Folder configurations is absolutely correct. So I asked myself what's the problem, after thinking I said that the installation of CS is not done correctly, something is missing.
So I begun in taking a look at CS installation. I discovered that there are two web-filters in IIS and they are referring to the same ISAPI filter file. That is the problem WebDAV tries to use both on the filters.
Please install Oracle Content Server correctly or don't install it at all.