During the process of a Full Import on the Active Directory Management Agent there is a reference on an Active Directory Organizational Unit to an Organizational Unit two levels down, the Synchronization Service Engine will crash.
A known issue in the Synchronization Service Engine.
Fixed in build 4.1.3479.0
A hotfix rollup package (build 4.1.3479.0) is available for Forefront Identity Manager 2010 R2
As of 10/30/2013, this fix is not yet ported to DirSync.