Hi all, I found the event error like the below: <failure trying to synch site aaaaaaaaaaaaaafor ContentDB bbbbbbbbbbbb WebApp ccccccccccccc. Exception message was Cannot insert duplicate key row in object 'dbo.UserMemberships' with unique index 'CX_UserMemberships_RecordId_MemberGroupId_SID'. The statement has been terminated..> I tried to do the step 1 under Sharepoint 2010 Management Powershell. It prompted an error message "Missing operation name or the operation name is invalid." when I run the preparetomove command. Seems like the command preparetomove does not exist in sharepoint 2010 now. 1. Run 'stsadm -o preparetomove -site <site collection path> - oldcontentdb <GUID of the contentdb listed in event log error>' 2. Run 'stsadm -o sync -deleteolddatabases 0'