title: iOS app crashing when calling alert message
body: <p>i have different apps where I use an alert message, so far never an issue.
  Now I get this error. I usually call the alertview from the didbecomeactive method.
  Can someone help me with this issue. Just getting started coding, so keep it slow :)
  Many thanks </p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSSetM length]: unrecognized selector sent to instance 0xa9737c0'
  </code></pre>