I did not get upgraded to F at the GM window on a SEA-SAN flight, and a FCM of $550 popped up. The following day, the FCM disappeared and the "FREE" error popped up. I called Delta and the agent told me there isn't any upgrades available and she's sending a ticket to Delta regarding the error. I did the unclick and reclick of the F upgrade request and voila, I'm in F now!