Rule 1. When you paste into the box to do a URL link (that's the box with 'http://' already in it) then paste OVER IT not AFTER IT.
Then you won't end up with too many http://http:// in the URL address. You only want to end up with one 'http://' . You are invariably posting two of them.
And of course, if you get it wrong the first time. Use the Edit button (that's the button with the pencil in the box) to do it right a second time.