How to resolve the "Camera in Use" error message is Yahoo! Messenger for Mac
This article provides troubleshooting steps for Mac users whose webcam won't work because it is "in use."
If you receive the "Camera in Use" error message, another application has control of your camera.
Try closing all applications that are currently running. Other applications may have crashed or exited without releasing your camera.
If this does not work, then simply restart your computer.