The mailboxes probably aren't synchronised with AD properly thats why they can't move in the AD Users and Computers
If you go to AD Users and Computers>Right click User>Properties>Exchange General
Where does it say the Mailbox is?
Example;
Server1 is Exchange 5.5
Server2 is Exchange 2000
Which Mailbox is it?
Server1/First Storage Group/Mailbox Store (SERVER1)
or
Server2/First Storage Group/Mailbox Store (SERVER2)
Are these AD Domain controllers on the same domain, replicating with each other?
During the Exchange 2000 install did you tell it that it was already part of an Exchange site and did it communicate properly with 5.5 during the install?
I did a migration once where as the site had 1 server with the lot on it (5.5 and the works...)
I installed a fresh 2kServer, upgraded the NT PDC to Win2ksvr, promoted it via 'dcpromo'
Installed and configured a 2way RCA (Recipient Connection Agreement) via the ADC, to synchronise the 5.5 mailboxes with AD.
to Establish a Connection Agreement:
1.On the Start menu, point to Programs, point to Administrative Tools, and then click Active Directory Connector.
2.In the console tree, click Active Directory Connector.
3.On the Action menu, point to New, and then click Recipient Connection Agreement to display the Properties dialog box. Use the information in the following table to fill in the boxes on the appropriate tabs, replacing servername_A with the name of the server the ADC is running on and servername_B with the name of the Exchange 5.5 Server:
General Tab - In the Name box, type servername_A-User-CA
For the Replication Direction, click Two-way.
To acknowledge the Exchange permissions warning, click OK.
Under Select a server to run the Connection Agreement, verify that servername_A is selected.
Connections Tab - Under Windows Server information, verify that servername_A is selected.
Under Windows Server Information, click Modify.
In the Connect as dialog box, click Browse.
Double-click Administrator or an account with the appropriate permissions.
In the password box, type the password,
To close the Connect as (Windows Server) dialog box, click OK.
In the Server box for Exchange Server Information, type servername_B
Verify that the Port number is 389. If you haven't changed the LDAP port then you will need to (do this in the 5.5 Administrator>Protocols>LDAP>Properties).
Under Exchange Server information, click Modify.
In the Connect as dialog box, click Browse.
Double-click Administrator or an account with the appropriate permissions.
In the password box, type the password.
To close the Connect as dialog box, click OK.
Schedule Tab - Click Always.
From Exchange Tab - To add an Exchange recipient container, click Add.
Expand the Site to Recipients.
Click the Recipients container.
To close the Choose a container dialog box, click OK.
To modify the Default Destination, click Modify.
To enter the Default Windows Location, expand domain.
Click Users (or the appropriate organizational unit), and then click OK.
To configure the objects that you want to synchronize, verify that all check boxes are checked in the Objects box.
From Windows Tab - To add a Windows organizational unit, click Add.
Expand domain.
Click Users (or the appropriate organizational unit), and then click OK.
To modify the Default Destination, click Modify.
To enter the Default Exchange Location, expand Exchange Site, and then select the Recipients container.
To close the Choose a container dialog box, click OK.
To configure the objects that you want to replicate, in the Objects box, clear the Contacts check box and the Groups check box.
Deletion Tab - Verify that Exchange and Active Directory objects will be deleted.
Advanced Tab - Verify that Windows Server entries per page and Exchange Server entries per page are both 20.
Verify that This is a primary connection agreement for the connected Exchange Organization is selected.
Verify that This is the primary connection agreement for the connected Windows domain is selected.
Verify that when replicating a mailbox whose Primary Windows Account does not exist in the domain, a Disabled Windows User account is created.
Verify that the initial replication direction for two-way Connection Agreements is From Exchange.
4. Click OK to establish the Connection Agreement.
5. If a message appears stating this is the first intra-organization connection agreement, click OK.
6. If a message appears stating that two security groups, Exchange Enterprise Servers and Exchange Domain Servers, have been created, click OK.
7. Close the Active Directory Connector Manager.
8. Verify that the Connection Agreement replicates before you install Exchange 2000 Server by checking mailbox locations.
Dcpromo'd the clean win2ksvr so that it started replicating AD with the upgraded PDC
Installed Exchange 2000 on the clean machine and told the install it was part of a current Exchange environment (don't forget to get it to install the 5.5 Administrator as well as the exch2k system manager on the new machine, as this is needed for the impending shutting down of the 5.5 box)
Configured Public folder replication with the exch2k machine via the Administrator program on the 5.5 box
after replication complete, rehomed them
Then did the 'Move Mailbox'
as easy as this
