Moving a mailbox within a single Exchange 2010 SP2 RU8 server failed repeatedly with error text like the following. Dismounting/remounting the database and running various New-MailboxRepairRequest commands did not fix the issue or provide guidance.
Error: MapiExceptionCallFailed: IExchangeFastTransferEx.TransferBuffer failed (hr=0x80004005, ec=1162)
Lid: 55847 EMSMDBPOOL.EcPoolSessionDoRpc called [length=3004]
Lid: 43559 EMSMDBPOOL.EcPoolSessionDoRpc returned [ec=0x0][length=685][latency=15]
Lid: 23226 — ROP Parse Start —
Lid: 27962 ROP: ropFXDstCopyConfig 
Lid: 27962 ROP: ropTellVersion 
Lid: 27962 ROP: ropFXDstPutBufferEx 
Lid: 17082 ROP Error: 0x48A
Lid: 21921 StoreEc: 0x48A
Lid: 27962 ROP: ropExtendedError 
Lid: 1494 —- Remote Context Beg —-
Lid: 1238 Remote Context Overflow
Lid: 1947 StoreEc: 0x48A
Lid: 1750 —- Remote Context End —-
Lid: 21817 ROP Failure: 0x48A
The mailbox’s failed Move Request Log in the EMC showed that the mailbox had 2819 folders total, which seemed high. There was also a Litigation Hold on the mailbox, which could be part of the problem. (In the past, a Litigation Hold in combination with an Exchange bug had resulted in a 1TB mailbox on our servers: a 2GB mailbox with 1TB of redundant calendar data.)
Opening the mailbox using OWA simply to check out those 2819 folder revealed the problem, a massive number of nested Junk E-mail folders totaling about 250MB.
After the folders were deleted using Outlook and OWA, the mailbox moved successfully. If deleting the folders using Outlook/OWA was impossible due to the sheer number of folders, then Outlook Cached Mode would have been tried next, then perhaps a server-side tool from Microsoft, and then possibly an IMAP client.