memory card problems

i purchased a 128mb of memory card from guitar center a couple of months ago, i still have 64.6 mbs left but now for some reason every time i try to save a sample, program, or sequence it reads directory error!!! and wont let me save. can anyone help me out with this problem its messing up my workload.............................

that just happend to me yeserday, i copied the shit to my computer, formated the card and reloaded the OS in the MPC. you could prbably skip the reloading the OS and be fine, it worked for me