If you go to the Fortress board, and click Ranking History, there is no such thing there.
http://www.wargear.net/boards/view/Fortress/Ranking%20History
"invalid data"
I pointed this issue out in the past on other boards.....
http://www.wargear.net/forum/showthread/4738/The_Walking_Dead_Stats
The reason is there have been no games finished on those boards in the last 60 days.