The synchronization error "extension-dll-exception" does not provide a great deal of information when viewed just from the synchronization service manager console. The exception is an indication that an exception has been thrown from the metaverse extension, most likely from provisioning code. The words extension-dll-exception is a hyperlink. To discover more about the extension-dll-exception, click on the words to open the Connector Space Object properties window.
A couple items to quickly review in this window is the Extension Rule and the Stack Trace button. The Stack Trace button is in the lower right of this window. The stack trace button will reveal even more information about the error message and display the stack that is being thrown. If the Stack Trace button is disabled, then take a look in the Application Event Log to see if you notice any further information.