Since you can’t access admin GUI you can do it by using utility: /opt/Avaya/MultimediaMessaging/2.1.0.0.833/CAS/2.1.0.0.833/bin/configureAMM.sh .
Then go to LDAP configuration and check configuration. Can you try to input credential again and reapply the settings. Then restart AMM (or it will be done by utility) and check if the issue is resolved.
Check spelling and make sure letters are capital when needed and nothing is missed.
In the JBoss logs we could see the system checking the roles and names and permissions, these should match what was programmed in the LDAP configuration utility. To collect the JBoss log
You can find it at /opt/Avaya/MultimediaMessaging/2.1.0.0.833/jboss-as/7.1.1/standalone/log