XADM: 0x8007203a Error Message Occurs When You Run SETUP /FORESTPREP in Exchange 2000

When you run Exchange 2000 Setup with the /forestprep switch to join an existing Exchange Server 5.5 site, you may receive the following error message:

This issue can occur if Exchange Server 5.5 is configured on a Windows 2000 domain controller, and both Active Directory and Exchange Server 5.5 Lightweight Directory Access Protocol (LDAP) ports are configured to use port 389.

When you configure an Exchange Server 5.5 computer on Windows 2000, you must manually change the default Exchange Server 5.5 LDAP port from 389 to another port that is not in use. To resolve this issue, change the port assignment for the Exchange Server LDAP service:

1. Start the Microsoft Exchange Server Administrator program, and then connect to the Exchange Server 5.5 computer that resides on the Windows 2000 domain controller.
2. Click to expand the following object:
   Site Name\Configuration\Servers\Protocols\LDAP (Directory) Settings
3. Start a command prompt, and then type netstat -an.
   
   When you run this command, a list of all the active ports that are listening on all interfaces is displayed. Choose a port number that does not conflict with any of these ports. Some common alternatives ports for LDAP are 390 or 391.
4. Disable the Use site defaults for all properties option.
   
   The server now reads the newly assigned LDAP port instead of using the port assignment from the site configuration.
5. Click OK, and then restart the Exchange Server directory service.

You are now able to run Setup with the /forestprep switch successfully.

Windows 2000 initializes the Active Directory LDAP service (port 389) before the Exchange Server 5.5 directory service starts. This service is configured to answer LDAP queries on port 389, by default. Because only one service may listen on a Transmission Control Protocol (TCP) port at a time, the Exchange Server 5.5 LDAP listener is blocked. This behavior causes Exchange 2000 Setup to fail to bind to the LDAP port for Exchange Server 5.5. When you change the LDAP port for Exchange Server 5.5 to a port other than 389, Exchange 2000 Setup successfully binds to the Exchange Server 5.5 directory service.