LG VX-8100

I have a Ridata mini SD card and for some reason when i put my music on it it only saves 10 or 13 songs!! (this is a 512 mb card!!!) on the list in the computer it shows all of the songs i put on it, but when i put it in my phone it only shows a few of them, i already checked the total amount of letters on the names (less than 47 characters) and all...do any body know why this happens??