Filesize can't be the issue here, as I myself also have a copy of Beek's tunes and they're all very-very-tiny (chiptunes... ^-^ wee!).
First try resaving, maybe indeed your copies are corrupt. Next try turning them into .j2b's. I know not everybody likes that format, but it's just for checking.
Or maybe you could post the files somewhere so we can take a peek?