Cannot move mailbox between Exchange 2000 and Exchange 2003

Hello,

One of our customers has two exchange servers. One Exchange 2000, migrated
from Exchange 5.5. Exchange 5.5 was previously Exchnage 5 and was upgraded
with in place upgrade.
Now their exchange organization is in native mode as there is no older
versions than exchange 2000. Before a month they installed in a new server
exchange 2003 with the purpose to move the mailboxes to the new server.
Unfortunately, when they try to move a mailbox between the servers using
Active Directory Users and Computers snap-in, in the step the wizard promts
you to select the destination server and mailbox store, the destination
server and mailbox store fields are blank and disabled.

Has anyone any idea?

Recently created mailboxes are moving between servers with no problem. They
told me that the mailboxes which cannot be moved are possibly created in
Exchange 5.5 or 5.

But I am still cannot find a solution.

Please send any idea..............

thanks,
Dimitris