After editing the LDAP Password field on the Administration Service - LDAP tab in the BlackBerry Server Configuration tool, you cannot log into the BlackBerry Administration Service using Active Directory authentication.
SOLUTION:
This is a known bug. See KB18161
Install BES 5.0.0 maintenance release 1 or reinstall the BlackBerry Administration Service again.
I solved it personally by immidiately updating to 5.0.1 MR1
