Hi,
Certainly strange. Just entering a license number should really not do this. The red image usually indicate no connection to the camera. When using RTSP the Test result should not indicate anything since the cmara do not respond to such a test so the green icons are not correct. If you change to MJPEG what happens. Testing for MJPEG works since the camera respond to that. Still green icons?
What do the Event Logs say? Is it red icons there are no connection to the camera. Still VLC is working though.
Since no camera is working I would do a clean installation. Use the installation program and Remove. The go to ProgramData-Moonware and delete all with Netcam Studio. Then go to ProgramFiles and Delete folder Netcam Studio. Now install NCS again. Add some cameras and check and the add the license and then continue to add cameras.
-Henrik