It appears there are major problems at the moment, as mentioned by quite a few people here: http://wibsite.com/board/topic/help. Basically the data that stored which user had what level of access to which blogs has disappeared. I’ve manually reset about 10% of you, but the rest will have to wait for a couple of days.
I’m really sorry about this, I don’t know how it happened but it may be omething to do with the system update I made on Friday night (WordPress MU 2.7.1, for those who are interested).
Anyway, I’m on the case and will get everyone back up and running as soon as I can.