I was given a work-around solution to this problem by an Apple employee at the genius bar in the Apple Store in Century City, California, which is in West Los Angeles. His name is Robert Stern. He thought that it might be a power problem. He said that instead of plugging the webcam into the computer directly, I should try plugging into a powered USB hub that is connected to my Mac Mini. It worked. He thought that the webcam needs more power to transmit video than it does audio. He thought that for some reason when the the computer comes back from being asleep only portion of the power the webcam needs is being given to the webcam. Therefore, the webcam can handle the audio portion of a video call via the webcam's microphone, but not the video portion of the call. He thought that by using the powered USB hub, the webcam never loses the full power it needs, even when the computer comes back from being asleep. Of course, I suggest using a USB 2.0 hub get the most out of your webcam. At some point perhaps Apple and Logitech will address this problem and fix it so that there is no need to plug the webcam into a powered hub and instead can be plugged directly into the Mac Mini. Until then, this is the best solution. Many thanks to Mr. Stern.