It's probably that the specific MP3 file or whichever song GT5 is trying to load next from the playlist / folder is "corrupt" as far as the game is concerned. I have had this problem, and after the "corrupt" song has been skipped and replaced with the regular in-game music, it goes right to the next song on my playlist. I have had whole albums skipped before because the PS3 / GT5 didn't like the way the files were encoded... so ya, that's my explanation / experience.
