I'm sure this has been asked before but I can't seem to find it. I recently booked an award ticket, using AA miles, to fly business class from JFK to LAX. I tried to use a BXP1 to upgrade - there was ample A space available - but was told it's not possible to upgrade an award ticket. Obviously, U class isn't listed as one of the fare classes ineligibly for upgrades, and before calling, I scoured the Business Extra site and found nothing prohibiting upgrading award tickets.

So could someone help me: is it truly prohibited to upgrade a U class award ticket using BXP1? Or did I just have a bad agent?