The 404 indicates that Facebook hadn't scraped your pages yet. When scraped, if your Open Graph tags are set up properly, then the error should disappear. Either you can scrape pages manually or wait for Facebook to do it. Sometimes this could be a short amount of time or could take weeks, depending on factors such as how much traffic your site gets, how new your site is, etc. Either way, there's not really anything we can do to make Facebook scrape all of the pages, except wait.
However, if you do think there is an issue with the Open Graph tags on the page, please let us know and we can help you investigate further.
-Melissa
404 Not found
