This means your camera is used by another software on your computer.
Please reboot your computer and have a try again. If still the same, Please check what software is already running after your computer is powered on.
Our user has reported software like 'YouCam', Logitech camera software, HP camera software, or Microsoft camera software running and preventing CamCam from getting the camera. After stopped these software or uninstalled them, CamCam works well.