criteria for ranking/xp recording

[screenfly]

hi, was just wondering what criteria is used for ranking or xp recording, i see lots of sessions in FARCRY when the icon in the trackbase says session not ranked or no xp recorded,i understand that with not enough players you dont rank,but even with a full server it shows no ranking or recording xp, could you explain this?
thnx and greetz
(and btw many thnx for still supporting our small Fc community)