only one BES server on a domain
That can be fixed by using a different DB name in SQL. When you uninstalled it probably didn't clear the DB from SQL.
I'm having the same activation issue though, and it doesn't appear to be anything wrong with permissions. I even went as far as adding besadmin into outlook to test its access to other mailboxes. Works fine.
BES just doesn't open the mailboxes to check them at all. Nothing in the logs either..
Have noticed these couple of entries in the eventlog though:
Unable to connect to Dispatcher 'ODYSSEY'
Could not connect to Service Control Manager at \\127.0.0.1: 1722