Serves me right for not fully reading your initial report... you quoted the error dialog saying this:
This application has requested the Runtime to terminate it in an unusual way.
That probably means that an unhandled exception was thrown. And the only thing that throws exceptions in Sigil is ZipArchive. It seems it couldn't read your zip file.
This could be a problem with the specific epub file, or a permission error. Calibre uses python's zipping utilities, and those can create bad zip files (I already had to create a workaround for such a problem).
Let's eliminate the epub file question. Download the epub file from this thread
and try to open it in Sigil. I know for a fact this one works just fine.