Moving exchange 2010 mailbox back to exchange 2007 server

Can you not do it from the E2k7 EMC?

You can do it in the Exchange 2007 Management console.

Move-Mailbox UserName –TargetDatabase “E2K7\First Storage Group\Mailbox Database” –Confirm:$false

Or all of them:
Get-Mailbox –Database “E2k10\First Storage Group\Mailbox Store (E2k10)” | Move-Mailbox –TargetDatabase “E2K7\First Storage Group\Mailbox Database” –MaxThreads 10

If i try doing it in Exch2007 console i get the following error :

Failed
Error:
Error was found for Stuart McIlwraith (STUARTM@cargocarriers.co.za) because: Error occurred in the step: Opening source mailbox. Failed to open mailbox with error: An unknown error has occurred., error code: -1056749262
Exchange Management Shell command attempted:
'CARGOJHB/Windows7/Users/Stuart McIlwraith' | move-mailbox -BadItemLimit '100000' -TargetDatabase 'SOYUZ\First Storage Group\Mailbox Database' -GlobalCatalog 'ibubesi.cargojhb' -DomainController 'ibubesi.cargojhb'

Does the account you are using have rights to the mailbox or the mailbox store? a simple test would be to see if it can open that mailbox with an outlook profile

give you user full mailbox access in the mailbox you are trying to move. go to AD Users and computers, choose advanced settings and go to the user security tab to give the appropriate permissons

Also make sure of the following:
Unhide from GAL.
Check that user is NOT disabled

Then try the move again

Yes the account does have full access to the mailbox, as far as i can see you cannot use the 2007 GUI or "Move-Mailbox" command to move a mailbox from 2010 back to 2007.

in 2010 they now use New-MoveRequest

Also make sure this key is not set:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\Disable MAPI Clients

Thanks for the update and the solution.