Hi!
I've had the same issues with WebDav on WinXP. It worked with http but not with https - the same
Code:
The folder you entered does not appear to be valid. Please choose another.
I tried the solution mentioned on the OpenXchange-page, in esssence search for "webfldrs.msi" in your windows folder, run it, choose the correct settings and reinstall webfolders in your system. Now https works for me in WinXP!
The problem is that you still need to install something on the majority of systems and for me I like that I can mount the briefcase as X: in Netdrive.
/K