We have noticed that third party cookies are not allowed in WebViews for iOS 5.1+.
To reproduce this issue create a new WebView and set the URL to http://m.na.se/Default.aspx?pageid=1179 this should show an ad, but just shows a blank window. Testing the same URL in the browser (both Safari on PC and iOS works, given that cookies are allowed).
Attached is the wanted result as a screenshot from the browser.
According to http://stackoverflow.com/questions/14448373/3rd-party-cookies-in-an-ios6-uiwebview this behaviour has changed as of iOS 6 but we can reproduce it in iOS 5 too.