The error can display as either DB11B or D11B Too many items in mailbox and occur at anytime during the migration process. The problem can be replicated using the Groupwise client and is a result of an issue logged with Novell.
A description of the error is foundhere:
Please contact Novell for resolving this issue prior to migration. Refer to this Novell support article for more information:
Upgrade the Groupwise client on the migration machine to prevent any issues with the migration.