How can I fix my Panasonic DMR-E55EB DVD recorder please?

My Panasonic DVD Recorder, model number DMR-E55EB/EBL, will record but will not finalize. It starts to finalize, then 40 seconds or so into the operation it stops, turns itself off then on again, SELF CHECK message is displayed. When I try to finalize, message on TV says CANNOT FINALIZE. Can anyone suggest what I can do to remedy this fault please.