Here's the problem:
my Mom deleted (well actually cut & pasted into another folder) some system FILES (such as RES_INFO.sys & SYS_CONF.sys) off of her Sansa Clip 2GB MP3. So I deleted everything off her player. I then added the system files back, but when I go to ADD the MUSIC back the computer won't let me because it still recognizes that the player has 1.5 (out of 1.8] being used. I think this is impossible. And I tried it on a Vista laptop as well as a Ubuntu desktop. Both give the same info about 1.5 GB being used but show a few tiny files or no files.

Does anyone know how I can get it to recognize as EMPTY so I can put her music back?  Try using the clip's format option to do a format on the device (UNLESS that's what you already tried???) .

I don't know the interface of the clip but on my Sansa Fuze 2GB mp3 player, you go to system options and then go to format and you'll be able to use the format function there. Clip probably has something similar.

On another thought, if that fails, perhaps you try updating the clip with the latest firmware with the sansa update software and give it a go.