When trying to open a "testfile" from an online bookshop (which is usually a brief extract of the beginning of the book, with a truncated or nonexistant .ncx) I get this error, and pressing OK, Sigil opens, but with an empty, new file. Since this type of error would be easily corrected in Sigil, shouldn't it just open the file with a warning?
I enclose the error and a typical file (which is an automatically generated testversion from my distributor of one my own publications, so no secrets or copyright issues here!).
9788779792661.epub
Other than that, I haven't encountered any errors in the latest beta - nice work!
Regards,
Kim