Yes, try to reformat it and after that check the integrity of the sd card. There are several tools for different platforms that do this. Are you running windows? Worst case scenario: a couple of sectors are damaged and the sd card will slowly lose more and more sectors to corruption and you will have to buy a new one. Or the file system is corrupted and everything will work fine again after a reformat.
Also: Are you trying to copy data to the sd card through the gp2x or and actual card reader?