As a last note. I have had similar issues where our 2 servers in the pool have been fighting over database control. When they do this they will not allow login to the BAS console.
This generally happens when the BAS service starts up on both hosts at the same time or so close that neither has time to register and take singleton access to the database.
I would check this with your environment. Stop the BAS service on all hosts. Start it on only 1. Wait till the service is fully loaded which is generally around the time it is using 400+Mb of ram. Attempt a login. If it is still failing contact RIM
If you can get in to the BAS with this method check the BAS pool protocol configuration.
Open Servers and Components \ Blackberry Domain \ Component View \ Blackberry Administration Service\
Transport protocol configuration
This may be set to multicast udp. Check if your BAS services on your hosts are running very high in cpu and memory. If so you may wish to change from Multicast to TCP with TCP Ping.
We had to take these actions with our environment.
Before doing any of this I would stronly suggest contacting RIM Technical Support if you are a subscriber.
Hope this points you in the right direction.