Rockbox Ports are now being developed for various digital audio players!
Actually, MP4dump has actually told you exactly what the error is (I think), that the metadata atom has an invalid size. Which would suggest that your encoder isn't creating the metadata properly.
$ mp4dump ./download/audio/75minutes_59.m4a mp4dump version 1.5.0.1MP4ERROR: Atom ReadProperties: atom is too small$
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