DVD RAM PANASONIC DMR-E75V WON'T ACCEPT NEW RAM DISKS

hello there experts, Can you help me. My dvd ram recorder refused to accept new blank disk. I get a message that the disk is not formated but if I try to format the disks it tells me that it is a locked and that I cannnot format it. I have tried 3 new disks. It works fine with my old ram disks and will reformat them but not the new ones! any ideas? thanks a lot and have a great day out there! Dan from Switzerland.