CNN says problem with Opportunity, no other sites confirm it.
CNN has had a story since this morning that Opportunity has a problem with a thermostat:
Mission manager Jim Erickson told reporters said the power loss appeared to be from one of the craft's heating units that keeps turning itself on and running overnight without receiving commands from NASA to do so.
While engineers do not believe the faulty thermostat will overheat the vehicle, the long-term consequences of the glitch and whether it can be fixed are not yet known, Erickson said.
For some reason no other web site I've seen has reported this.