The domain where your application is hosted must be SSL certified (https) eg: https://my-domain.com/my-app. Else, your app can't be published in facebook.
Btw, in the App Settings you have to give this in the Secure Canvas URL too, eg:
Canvas Url: http://my-domain.com/my-app
Secure Canvas Url: https://my-domain.com/my-app
What did you wrote in these settings?