title: iAd banner not loading ads
body: <p>This is more of a post than a question but thought I would share my experience because I just struggled with this for a number of hours.  I didn't see anything in the documentation or other SO posts but I may have just overlooked it.  Anyway, I have a view controller with an AdBannerView shown at the bottom of the screen.  I set up the banner through the storyboard including Auto Layout constraints to the left, right and bottom.  I wouldn't see any ads during testing and I kept getting the error ADErrorDomain - code:3 "The operation couldn’t be completed. Ad inventory unavailable"</p>
  
  <p>I finally figured out it was my Auto Layout trailing space constraint that was causing the problem.  I'm guessing this was creating an adbanner with dimensions that did not match any available ads.  Once I removed the Trailing Space constraint the test ads displayed correctly.</p>