From the Independent Online:
"......Mr Clark confirmed Emirates is cancelling an order for 18 long-range Airbus A340-600 aircraft as it had decided they were no longer suitable for its route expansion plans. This is likely to form part of the compensation negotiations with Airbus."
and from
http://msnbc.msn.com/id/15449014/
".....The airline has already had difficult experiences as an early launch customer for a previous Airbus aircraft, the ultra-long range A340-500, where the wings were too heavy on the early versions.
In a very unusual move Mr Clark said that the airline had also cancelled previously placed firm orders for 12 of the large capacity, long range A340-600 (high gross weight) aircraft.
Maurice Flanagan, Emirates deputy chairman, said that the A340-600 HGW could not meet the performance needs of the airline for services from Dubai to Los Angeles, and Airbus had already agreed to refund $160m of pre-delivery payments in a deal that was "ring-fenced" from the negotiations still to be held on the A380."