After installing BES USer Admin Tool (BESUserAdminService and BESUSerAdminClient) on my BES 5 from Blackberry Resource Kit 5.0, I ran this command to generate BESUserAdminClient password.
Where 'admin' is the BES login created at the time of BES installation with password 'adminPwd'. 'clientPwd' will be used in all commands of BESUserAdminClient.exet like