Ben Winzez blogged about some errors during the move mailbox process and some ways to avoid those errors.
I wanted to bring to light a specific issue that may occur during mailbox moves in complex environments with multiple Active Directory Sites and multiple Exchange servers. There are several other settings which must be in place in order for this issue to present itself.
First, here are the settings which need to be in place:
1. On both the Source and Target mailbox stores, set Deleted Mailbox Retention to 0 days.
2. Note what the Online Maintenance schedule is set to on both stores. The moves need to be scheduled to coincide with Online Maintenance on the Target mailbox store.
*Note - for the purposes of my testing, I set Online Maintenance to run Always for my databases.
3. There must be multiple Active Directory Sites so as to introduce AD replication latency (Inter-Site connectors can only replicate every 15 minutes), and there need to be Exchange servers in these different AD sites (or Exchange must be configured to statically point to the GC of the other site).
4. Enable Diagnostics Logging under MSExchangeIS\Mailbox, and set the category General to Maximum (only minimum is necessary though). This is necessary in order to log Online Maintenance events.
Read more at source: http://msexchangeteam.com/archive/2009/01/30/450549.aspx