ERROR 1066: Unable to open iterator for alias – Pig

Are you running a pig 0.12.0 or earlier jar against hadoop 2.2, if this is the case then
I managed to get around this error by recompiling the pig jar from src, here is a summary of the steps involved on a debian type box

1. download the pig-0.12.0.tar.gz

2. unpack the jar and set permissions

3. then inside the unpacked directory compile the src with 'ant clean jar -Dhadoopversion=23'

then you need to get the jar on your class-path in maven, for example, in the
same directory

mvn install:install-file -Dfile=pig.jar -DgroupId={set a groupId}-
                 DartifactId={set a artifactId} -Dversion=1.0 -Dpackaging=jar  

or if in eclipse then add jar as external libary/dependency

I was getting your exact trace trying to run pig 12 in a hadoop 2.2.0 and the above steps worked for me

UPDATE
I posted my issue on the pig jira and they responded. They have a pig jar already compiled for hadoop2 pig-h2.jar here http://search.maven.org/#artifactdetails|org.apache.pig|pig|0.12.0|jar
a maven tag for this jar is

  <dependency>
       <groupId>org.apache.pig</groupId>
       <artifactId>pig</artifactId>
      <classifier>h2</classifier>
      <version>0.12.0</version>
      <scope>provided</scope>
  </dependency>