weird CopyOnWriteArraySet error

I'm getting a java.util.NoSuchElementException at high loads using
java.util.concurrent.CopyOnWriteArraySet. I have one guess why and
would like to hear if it makes sense. Could this error occur because
two threads call the same instance?

For example, thread A executes i.hasNext() which returns true. Then
thread B runs and happens to start executing at i.next(). When thread
A runs again, it will execute the i.next() but B has already advanced
the iterator to the end of the list.

I'm using CopyOnWriteArraySet to avoid synchronizing. Do I have to
sync to avoid this issue?

Thanks for the opinions!

public class DistributionSet extends CopyOnWriteArraySet {

   private Iterator i;

  public void enqueue( Object message ) {

           for ( i = this.iterator( ) ; i.hasNext( ) ; ) {

            // .next() call is throwing an error - why? either:
            // copy hasn't completed or .hasNext() has a different
count, or some listener was removed
            EventListener listener = ( EventListener ) i.next( );
             listener.eventObserved( message ) ;

        }
  }

   public boolean add( EventListener consumer ) {
                  super.add( consumer );
         return true;

    }
}