Won't record, looks empty, but says it's almost full

I'm getting an error message when i turn my olympus ws-300m on that says, "C'.ant Make The System File. Connect To PC And Delete Unnecessary File." no matter what button i push, this message will not go away.
when i connect to my mac it does not have any folders or files in it when i double click on it. however, when i get info it says the capacity is 249.8 MB and 32 KB are available.
i think i may have removed necessary files from it on accident by dragging and dropping all files the last time i transferred data. i tried to drag and drop those files back into the recorder, but it says there isn't enough space to copy them onto it.
what can i do to restore my machine so it will work again?
please help.