Your epub has an embedded .psd (Photoshop Document) file in the images directory. Sigil will not show the file in the browser.
There are several ways of removing this file. You could try removing the file manually using a zip utility to open the epub and delete it, you could install Doitsu's
DeleteUnmanifestedFiles plugin or if you also use calibre, you can use it's
Modify ePub plugin to remove unmanifested files.
After this, I would contact whomever gave you that epub and beat them severely with a soggy wet noodle.