Usually, this could be either a problem with the USB cable, or with the connectors. The mini-USB connector on the camera is not designed to handle mechanical stress. If you are moving the camera around to look at various objects, it can sometimes disconnect (even though the connector is still plugged in, the connection gets temporarily broken). Usually when we give demos where the camera moves a lot, we mount it on a tripod and we secure the USB cable to one leg of the tripod so that it will not move at all at the connector when the tripod is moved. Some First Robotics teams have designed mounts with strain relief. Look for 'jevois' at thingiverse.com, for example this one:
which also has a mount for a ring of LEDs (for night/IR vision).
If the problem occurs when the camera is not moving at all, then the next likely cause is a bad USB cable. We have had a few reports of bad cables. We have changed cable brand since then but maybe try another cable if you have one around.