I was having the same issue 1 day on my mage then another on my resto shaman (both 570+) I really don't think it has anything to do with your "rating" at all....it may be they already have enough locks in the group and need another class. If the WL is getting full they kick people they don't need so there is room for the potential ones they do need. I know its frustrating, but 10 days w/ oqueue has made me wish that I hadn't been so silly for so long and just tried it 8 mo. ago when i first heard about it. Give it a chance some of the groups you will get will make you glad you did.