Application log: Event ID 41111
The Exchange mailbox provisioning task failed during processing of a mailbox. The process will continue.
Error: SqlDateTime overflow.
Use ADSIEDIT and run it as the Vault Service Account.
Check if you can see the "whenCreated" and "whenChanged" attributes. If they are blank than this is the problem. You don't have suffucient permissions.
Give extra rights to Authenticated Users
Grant the Windows special group 'Authenticated Users' the permission 'Read All Properties':