XADM: Error Message When You Run Setup or Setup with forestprep Switch: "This Account Must Be Valid Before Continuing"

When you run Microsoft Exchange Server Setup, or you run setup /forestprep, the setup program may not be successful. You receive the following error message:

This problem may occur if you are joining an existing Microsoft Exchange Server 5.5 organization. For the startup account for Exchange 5.5 services on the existing Exchange 5.5 server, you are using the User Principal Name (UPN) (for example, user@domain.com) instead of domain\username to log on to your Exchange 5.5 Services.

To resolve this problem, follow these steps.

NOTE: Follow these steps on the Exchange 5.5 server that you designate when you join the organization. This article assumes that the Exchange 5.5 server is running Windows 2000.

1. Right-click My Computer, click Manage, double-click Services and Applications, and then double-click Services.
3. Change the logon as, for the startup of all MSExchange 5.5 services from UPN (user@domain.com) to domain\username.
4. In the properties of the service, click the Startup tab, and then manually type the domain\username that you want to use.
   
   NOTE: Do not browse to select the account for services startup. If you do, it will default to UPN, and you will not be able to manually modify the account information without quitting Services, and then restarting them.
5. Restart the MSExchange 5.5 services.

The resolution works because forestprep sends the account that you enter when you joining the Exchange 5.5 organization to the Exchange 5.5 server for validation. When Exchange Server Setup is set as domain\username, Exchange Server 5.5 can authenticate the user.