OGM autodeletion digitor F-8013

Question

Very often our digitor F-8013 will delete the outgoing message of its' own accord, either whilst it is switched off or overnight whilst the unit is still on. This results in patients calling in and receiving the standard message. I have a 9volt battery in the back as a back up power supply. Also sometimes the unit displays Cr, and I cannot find this in the instruction manuel. Do you have any ideas as to what the problem may be?