In some cases after configuring the User Profile Synchronization Service in SharePoint 2010 you get stuck trying to figure out where the snag is in the sync process. In most cases there are no real errors displayed in the interface, while something went wrong in the process. The troubleshooting solution is the ForeFront Identity Manager Synchronization Service Manager tool.
This tool provides you more insight into every step of the sync steps and process providing detailed result status for each step. Double-clicking on each entry provides you more details including a nice error description if there was one. This saved my life a few times.
Most of the errors I have run into are related to AD permissions for the UP service account. You can find this tool under the path:
C:\Program Files\Microsoft Office Servers\14.0\Synchronization Service\UIShell\miisclient.exe
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