That is not a fault with the device. The problem is happening while the KoboTouchExtended driver is doing its work. It has to open the book to make the changes to convert it to a kepub. The book appears to have an embedded font that is obfuscated. Unfortunately, the obfuscation key for the font can't be found. Without seeing the book, I can't say anything else about why this would be the case.
I suggest you report this in the extended driver thread. The error with the book won't be fixable there, but, the error can be caught and treated like other encrypted books.
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