I have just recently downloaded and uploaded the SimpleSDAudio Library from this website and tried the Bare Minimum with Debug sample. I tried it a few times and it worked great, but after about 9 times of using it, the thing stopped, saying "MUSICSAMPLEAUD.WAV not found on card! Error code: 1" The file was on there and SD Card wasn't locked or jammed.Thanks!
The only thing i mainly changed was using an SD Card shield instead of an SD Card itself.
EDIT: Nevermind! All of a sudden worked!