Memory card / wave free?

when i go into the memory card from my pc, all the files i want are there. but when i go to load them from the mpc into a program, some files are no where to be found. i tried deleting some old samples (wavs) from the card thinking this might free up space for the others to load. no luck. from the load page the "wave free" stays the same. i have plenty of space on my memory card. could i just be loading corrupted files? when i deleted one i thought might be corrupt, a sample i was trying to load previously, appeared in the load list. i don't know if i am explaining it right.
any help?

jjos1/1000

You may have to format card? And make sure those Wav files are 16Bit and not 24Bit

do the format in the mpc not in the pc. and wav format is pretty important too.