title: ERROR 1066: Unable to open iterator for alias in Pig, Generic solution
body: <p>A very common, error message in Apache Pig is:</p>
  
  <blockquote>
    <p>ERROR 1066: Unable to open iterator for alias</p>
  </blockquote>
  
  <p>There are several questions where this error is mentioned, but none of them give a generic approach for dealing with it. Hence this question:</p>
  
  <p>What to do when you get an ERROR 1066: Unable to open iterator for alias ?</p>