I faced with an error: Imported Failed – We couldn’t find a feed using the URL you provided when I tried to import my RSS feed in WordPress CMS to Facebook.
I’m sure my feed is valid because it was generated by WordPress, I trust WordPress 🙂
After I tried with 3-5 times, it worked :). The solution is very simple, it may had some issue on Facebook system, just try few time and everything should be fine 😀