This happened to me about 6 times in 2004. I went to checkin online and it wouldn't let me because my outbound flight hadn't cleared my reservation (it was still listed even though I had flown it and the miles had posted to my account). This only happened on when my return as within about 24 hours of less of my outbound flight. I'd call SMS and the agent would clear the outbound leg, but the miles would disappear from my account. I once had the agent see it first-hand as he/she cleared my outbound flight from the reservation.

However, each time after calling SMS they would call "down to the service cetner" and request flight credit and it posted in a day or two. So, I'm not sure what they are having a hard time posting your outbound flight. But wanted you to know that others are having the same problem.

Happydad