It is under HKCU\Software\RealVNC I got the same issue and now it works. You should run VNC (user mode) in your PC, configure portnumber, password (ex: 5000, 1) and copy the above key. Copy exe and dll files inside the VNC folders into system32 of WinPE3. import the key using reg in WinPE3 then start winvnc4, it will hang there waiting for connection. from your PC, type vnviewer 10.10.1.1::5000 , a box appear, type password 1 ( I do not see a need of hex or binary). that is it. Not sure if you solved it or not. Just hope it help as I got help from others.
