File a bug report and give me all the requested information. My access is sporadic at the moment, and will likely continue to be sporadic for the next few weeks, but I'll see what I can do.
In the meantime (and AFTER you file a bug and give me all the information I need) you may be able to resolve this by using the Modify Epub plugin. Specifically, if this is caused by what I think it is, you want these modifications:
- Removing missing file entries from the .opf manifest
- Add unmanifested files to manifest
The first one is the important one, the second is a precaution but I recommend doing both at once.
If you obtained this book from an online retailer, I would recommend also going back to the store you purchased it from and telling them that the book has errors in the ePub TOC data, possibly also the ePub spine data.