Resolution:
When authorization is enabled and the two EMS Servers are configured in FT mode, both EMS Servers must have the same server name and password. In addition, there must also be a user (in users.conf) with the same name as the EMS Server name ("server" parameter in tibemsd.conf). The user's password must be the same as the server's password.

If these 2 EMS Servers are not sharing the users.conf file, make sure that you create an user with the same name as the EMS Server, and set the user's password with the value of the "server" password.

Let's say we have two EMS FT Servers (Server 1 and Server 2), the server name is "EMS-SERVER", here are the steps:

(a). from the active (Server 1), use the tibemsadmin tool:

set server password=&ltserver_password>
create user EMS-SERVER password=&ltserver_password> (if the user "EMS-SERVER" is not already created)

(b). from the backup (Server 2):

Same as step (a)

(c). from the active (Server 1):

set server authorization=enabled

(d). from the backup (Server 2):

Same as step (c)

Since two EMS servers running in FT mode should have the same configuration, if you create username and password for a user, you should do it for both EMS Servers. Otherwise, in some situations, the first server (first one to be up and running) cannot authorize and verify user credentials and permissions to the second server if they do not have the same server/user password configuration.