I have an NET MD MZ-N505 too and have the same problem. A few days ago it started NOT to record. When i tryed to record using SonicStage, the disc appeared in menu and the music was transfered. But when i turned off the MD, i lost all files and the disk appeared blank. I've tried it with used and new disc. My unit has died? Or i have done something wrong in the configuration? Becouse a few days ago it recorded a disk with no problem. I don´t know what happened.....