I have 5 Panasonic branded DVD-RAM 3x non-cartridge discs.
(DVD Identifier shows Manufacturer is “Matsushita Electric Industrial Co. Ltd”)
They all worked fine for over a year, but only had about 3 recordings each.
Recently, 2 of these gave the “UNFORMAT” error on the DMR-ES20DEB.
I tried formatting - no joy.
Tried formatting on XP in DVD-RAM drive (LG) - no joy
Tried formatting on Vista in DVD-RAM drive (Lite-On) - no joy
What are you using to format them on the PC? You’d want the Panasonic RAM driver in XP, and check the discs for write-protection. (WPTool)