The WC7665 is a bit of a Frankenstein... it's Docucolor 250 chassis with a new user interface bolted on, and the integration is... less than seamless.
I've had two of them. The first one had the problem you're describing at least three times a day. Xerox eventually replaced the machine under their guarantee, and the second one is doing much better (error shows up every week or two, and automatically corrects itself when it does.)
The short answer to your problem is: turn off the copier, wait a couple of minutes, then turn it back on. If this doesn't work, check the USB cable between the controller (mounted on the back of the chassis) and the user interface. With my first machine, I found that if the problem survived a reboot, swapping the cable to a different USB port would clear up the error for a while.
For a longer term solution, I would start logging service calls whenever you see this happen. Since we're talking about a fairly recent machine here, I think it's fair to say that you're probably still leasing/financing it. If that's the case, the repeated service calls will eventually result in your problems being escalated, and (probably) the machine being replaced.