Thanks for the reply! Appreciate it much.
BA doesn't show that it & or its partners fly between BOS & ANC. It may be giving a wrong error message when the issue is the fact that there are no 12.5K awards. Its 20K awards (each way) that I see few weeks before and after my chosen dates of travel (Jun 27-Jul 6).
Unfortunately, my travel dates are not flexible.
I don't have SPG. I can transfer from AmEx MR to SPG and then to Alaska, can't I?