Problem copying sounds to flash card

i have a external flash drive that i put my mpc memory card in to copy sounds to it from my computer. sometimes when i copy a lot of sounds it starts saying "error copying file or folder cannot copy (name of file): the directory cannot be created." i tried to reformat the external drive and copy everything again but then it gives me the same message with a different sound. its never the same sound twice. its kinda frustrating n i dont know what to do, anyone have any ideas?

i noticed somethin that might help my problem. i have a 128mb card and the sounds im tryin to put onto the card are only about 30mb, but when i have around 375 items loaded onto the card is when i start getting the error that the directory cant be created. just thought that bit of info might help someone figure out my problem.