HI, i'm a new omd owner and have purchased a 20mm Panasonic lens. I have found sometimes the camera won't let me take a shot. The viewfinder/screen shows grey with no shutter response. It then gives me the message 'remove usb' It sometimes clears when shutter is depressed, sometimes not. If I put on the kit lens , it functions normally. Any ideas would be appreciated. Kind regards Russ.