Lots of file errors, O also now can't copy files off, says i/o device error

try using a memory card with 2GB or below
the camera might be having some problems reading the 4GB that you have

if you connect the camera to your computer and file error still appears that means that the memory card is corrupted and you really need to format it

before you do make sure that you have a copy of the files saved in the memory card

*formatting the memory card will delete all the files saved in it

go to MENU> SET UP > FORMAT