The Chrome web store seems to have made a recent change to the contents of the generated extension (CRX) file.
There is a new _metadata folder being added by the Chrome Web Store, not by people like me who are writing Chrome extensions.
Older Chrome based browsers are getting the error because they didn't allow files with a leading underscore to be part of the extension package. Unfortunately, there's nothing I can do about it until the other browsers, such as Iron, Blackhawk, etc allow the new folder.
ALSO, I apologize for my replies taking a bit to show up here. I AM listening but, I'm still new so they all have to be approved by a Moderator.