[Bodhost-Andy]

Error: Connecting to destination server. cn=newuser,,CN=Users,DC=regency,DC=com The attempt to log on to the Microsoft Exchange Server computer has failed. The MAPI provider failed. Microsoft Exchange Server Information Store ID no: 8004011d-0512-00000000

Above error message can come when you use the Active directory and snap in to migrate Exchange 2003 user from one server to another server That error comes because migrate mailboxs can't log on to the system attendant mailbox.
The system attendant mailbox usually on the default mailbox store.

Solution :-Default mailbox store should be mounted.

You can use following steps to mount mailboxes in Exchange server 2003

1.Click on Start -> Click Programs -> Microsoft Exchange -> System Manager.

2.Open the First Organization -> Servers -> ComputerName -> First Storage Group.

3.Inspect the icon Mailbox Store. If there is a red X on the icon, you need to mount the mailbox store. (If there is no red X skip to step 5.)

4.Right-click on Mailbox Store and select Mount Store. This will mount the private mailbox store.

5.To verify that the store has been mounted, right-click on Mailbox Store. Select Refresh. This will allow you to open the item and display the user mailbox names.

6.Inspect the icon Public Folder Store. If there is a red X on the icon, you need to mount the public folder store. (If there is no red X skip to step 8.)

7.Right-click on Public Folder Store and select Mount Store. This will mount the public folder store.

8.To verify that the public store has been mounted, right-click on Public Folder Store. Select Refresh. This will allow you to open the item and display the public folder names.