I tried a few things after exporting the .wdgt file (I went into the file structure of the wdgt file to do these things):
- deleting files with the & character (no change)
- deleting additional .js and the ‘license’ file which had no file extension
- re-encoding mp3s (One of them was an mp3 with extended attributes which included a ‘cover photo’ linked to the mp3 file… no change)
- deleting m4a files (this worked!)
So then I re-encoded all of the m4a files in the Hype file by opening it up, (ctrl + click and then re-encoding all of the m4a files). Then re-exporting the .wdgt.
I used ‘permute’ to do this in a batch, but the problem is likely one of those .m4a files is not being recognized as an m4a file by the creature behind the iBooks Author curtain validating files: https://www.dropbox.com/sh/4kda8lk3iei9tgv/AADZrCy9XJLiFdvs69kuSo6Ja?dl=0