I suppose this should do:
INSERT INTO SurveyInterface.tblLoadISFNotification (OperatingEntityNumber, SDDS, SurveyCodeId, QuestionnaireTypeCodeId, ReferencePeriod, DataReplacementIndicator, PrecontactFlag, SampledUnitPriority)
SELECT
OperatingEntityNumber
,[SDDS]
,[SurveyCodeId]
,[QuestionnaireTypeCodeId]
,[ReferencePeriod]
,[DataReplacementIndicator]
,[PrecontactFlag]
,[SampledUnitPriority]
FROM (
SELECT
cnt = COUNT(*) OVER (PARTITION BY ISF.OperatingEntityNumber, ISF.QuestionnaireTypeCodeId),
ISF.OperatingEntityNumber
,[SDDS]
,[SurveyCodeId]
,[QuestionnaireTypeCodeId]
,[ReferencePeriod]
,[DataReplacementIndicator]
,[PrecontactFlag]
,[SampledUnitPriority]
FROM dbo.tblISF40201507 ISF
JOIN Operating.tblOperating O
ON O.OperatingEntityNumber = ISF.OperatingEntityNumber
JOIN Operating.tblAccountingTypeCharacteristic ATC
ON O.OperatingId = ATC.Operatingid
WHERE atc.AccountingTypeCharacteristicCodeId = 3 -- Allocation Entity
) AS duplicates
WHERE cnt > 1
-- Gianluca Sartori