This is a great tools that was released a couple of months ago. It could be a good idea to run idFix in the startup of the project to find and eliminate possible problems as soon as possible.

http://www.microsoft.com/en-us/download/details.aspx?id=36832

IdFix is used to perform discovery and remediation of identity objects and their attributes in an on-premises Active Directory environment in preparation for migration to Office 365. IdFix is intended for the Active Directory administrators responsible for DirSync with the Office 365 service.