Can't continue playing mp3 files from playlist when the phone is locked

[Abzoozy]

Can't VLC play multiple mp3 files in the background when the phone is locked? Every time one mp3 ends, the app just always fails to play the next one automatically. When I unlock the phone and open the app up again it says:

File reading failed VLC could not open the file xxxxx/xxx/xxx (operation not permitted).

Please help. It only happens if the files are of MP3 type.
If they are videos or MP4 it jumps between them with no problem.