Removable disk says "there is not enough space on disk" but there is! HELP?

I'm trying to transfer music by using a removable disk- I successfully transferred 84 songs, but when I put the disk back into the computer after I had deleted all of the files off of it, it tells me that there is no space on the disk, when there is NOTHING on the disk. How do I resolve this! If it helps, I'm using a Windows XP computer, but I tried it on a Mac and I have the same problem.