I'm searching for Award availability on routes between SEA and LHR using Amadeus/OneWorld and I can see the availability from LHR to SEA on BA with no difficulty, but whenever I try to search for SEA to LHR, I get the error message which states, "Award availability cannot be checked for the specified origin and/or destination. Please checked extended and try again..."

I've got the extended mode checked, and it works flawlessly for the opposite directions. Any ideas?