[Magnuss]

Originally Posted by Jaws;4601538
That said, my experience in the past has been that the "upgrade internals" option, which is checked on the first of the screenshots, is most likely to be related to any later errors. That's far less because of Calibre than some of the idiosyncratic coding and workarounds often found in epubs (example: books that use [CODE

<div>[/CODE] instead of

<p>

for every paragraph) that makes it difficult to properly update from epub2 to epub3.

Thus, the first step I'd take to debug this is to uncheck "upgrade internals," close everything, restart everything, and try again.

I checked it without upgrading the internals, and it crashed anyway. I also tried using three random books each time and it didn't matter which books I chose; they crashed anyway. If I did them one at a time, they didn't crash. Thank you for the suggestion.