I have had similar problems with my 2005 Shaker. Just keep pressing the eject button and turning the radio off and on, and it will eventually eject the CDs and get out of the error mode. Its tedious, but has worked every time.
The problem seems to be a keep alive memory relay that sticks when you turn the car off. It leaves power to the CD, but not the rest of the radio (why?), and the CD starts cycling after you leave the car. Sometimes I got back in the car and could hear the CDs changing inside the head unit. It eventually drains the battery completely.
My solution: Before you shut down the car using the ignition switch, shut down the radio first so it only displays the clock. This seems to break the cycle with the relay and the CDs. If you leave the car for an extended period, I would first eject all the CDs. That prevents the error because there are no CDs to cycle through.
Its not an elegant solution, but its worked well for the last two years.