Open a case with Quest Support (Support@Quest.com) for assistance with resolving this issue.
Before opening a case stop synchronization and back up the ADAM instance as described in Solution 10061 "Information required for troubleshooting DSA (Directory Service Agent) issues.": http://questsupportlink.quest.com/eSupport/Solution.asp?WAid=268451283&itemID=10061
After resolving the issue all OUs in source or target scope will be unselected and synchronization scope has to be configured again (only the scope, all the settings of synchronization will remain untouched) and a Full Resynchronization will be required.