One of the agents (MTA) reports in the log:
15/05/2012 14:46:11 PowerShellCmdExec::Inuit Error -2147467259 Processing data from remote server failed with the following error message: Only administrators can override the Thread Options remotely. For more information, see the about_Remote_Troubleshooting Help topic.
But when using the powershell from the agent host where the MTA is installed the mailbox can be moved without any problems.
Insufficient rights.
Documentation explains: Accounts Used by Migration Manager for Exchange Agents
Membership in the local Administrators group on all target Exchange servers involved in the migration. If a server is a domain controller, the account should be added to the domain local Administrators group of the domain.
Add the account to the local Administrators group on the target Exchange servers.
