[KevinH]

Hi,
I will edit your content.opf and post it for you to use as a model. Will you try rerunning epub3-tizer on your valid epub2 version and saving it under a new name. Then rename the new epub output from epub3-itizer to end with .zip and unzip it and post just the unzipped content.opf file here. That way we can see if the problem is with Epub3-itizer or Sigil.

Thanks,
KevinH

Update: see below for a content_fixed.opf you can use to hand correct your version.

As for your warnings, I see under the manifest properties that svg is being used heavily in this epub. If you use svg and there are links in it you should add the xlink:title property as mentioned in the warning.

Also, how are you checking the epub2 version before running epub3-itizer? Are you using the FlightCrew plugin or the epubcheck plugin? Given the preponderance of svg in this file you should probably use the epubcheck plugin to do your epub 2 checking as well. Also remember that epubcheck warnings are NOT the same as errors in any way.

KevinH