Your upstream power levels are out of spec. Typically this is caused by a wiring issue. It could also be something on Comcast's end.
See: troubleshooting guide.
Tip: If you need service, sign up for the Service Protection Plan (SPP). It's around $6 a month and you must keep it for at least 60 days after your service call. If you have SPP, you won't incur a service charge. You can sign up when you schedule an appointment.