Obviously this applies to both games, but there are certain ads that are bugged so that they never give crowns, namely, the ones that tell you to "Explore great content" The timer thing that appears in the window in game doesnt do anything, and none of the pages it links to seem to have any way of communicating with the ad. It's kind of a nuisince since there are a lot of verions of this ad that get in the way of the ones that do have a payoff.
If this is happening when you click an ad that opens a browser window, follow the directions in the browser window outside of Wizard101 to continue viewing the content. It will then progress and you will see that you completed the video and earned the crowns in game.