Open LDAP Admin. Create a new connection to LDAP server and use exactly the same information used in ALM to connect it to the LDAP server (Host name, Base DN, Authentication info, etc).
Connect to LDAP server. If the connection also fails with this tool, so the root cause should come from LDAP and network connection problem. You can use this user friendly tool to make it work properly before attempting once again from ALM.
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