Sigil can't load the ePub when they contain a relative path:
Code:
Possible evil or corrupt epub file name: OEBPS/../images/cover.jpg
The attached ePub is also the worst case, because it contains the same file with a valid file (but only the relative path is buggy, not the duplicate entry).
It's rare, and I'm sure in some cases the error is valid and nothing can be done (when you exit the archive for example).
PS: the bug is old. Ironically it was "quite" easy to find a ePub with this : The "Quick start guide for Calibre" 4e edition -by John Schember.