I have TightVNC Server (v. 2.7.10) running on my computer (Windows 8.1 Professional). When I am physically at the computer, others can see my screen using a VNC client. However, when I RDP into my computer, other users cannot view my session; they only see the Windows lock screen.
How can I enable other users to see my current RDP session using TightVNC?
VNC and RDP are different protocols. VNC is screen sharing, with the option of using a client's input (i.e. mouse, keyboard, etc) on the server's screen, with the server's controls still active. Remote Desktop was made for administering the computer, which started out with NT4's Terminal Services. It was part of what made Windows a multi-user environment, as each user has their own session.
When you RDP, it locks out the console on Consumer versions of Windows. For the Server editions, it does not kick off whoever is at the "console". You can over ride this by using the /admin (used to be /console) command when running mstsc.exe.
If you are using VNC, you are seeing the console's screen. If you are using RDP, you are connecting to a session. In the case of Windows Professional editions (not the servers!), you are only allowed one concurrent connection, so it locks the console's session when someone connects. There is no way around it.
There are solutions... but each of them has limitations:
You have to launch VNC Server on the remote session as "application" instead of "service". In this way, you can see the RDP session but you can't interact with its UAC.
Another solution is to launch the VNC server on the computer from which you start the RDP connection to the remote computer, in this way the remote user can see the client's RDP window and use it.
3. Added 2021: TightVNC Server from the version 2.8.53 support connection to an active RDP Session. (but you have to disable query to "accept/reject") source
(voice-over) 10 years later:
Enable Connect to RDP session option in server settings. Works flawlessly at least in non-server versions of windows while allowing tightVNC to run as a service.
Im not sure if it will work, but try to run the TightVNC standalone server from your RDP, don't run the TightVNC service (I'm guessing, that with the default install, you chose to have the service running).