I am attempting to a drop down list to a cell which is populated from a range of cells held on another sheet

At the moment I am using the Validation method and can successfully populate from a comma delimited string but not from a range that I have from another sheet

Excel::ValidationPtr pValidation = pRange-Validation

pValidation-Delete()
pValidation-Add(Excel::xlValidateList, (CComVariant)xlValidAlertStop, (CComVariant)Excel::xlBetween, (_variant_t)str)
pValidation-IgnoreBlank = VARIANT_TRUE
pValidation-InCellDropdown = VARIANT_TRUE
pValidation-InputTitle = OLESTR("")
pValidation-ErrorMessage = OLESTR("")
pValidation-ShowInput = VARIANT_FALSE
pValidation-ShowError = VARIANT_TRUE

Regards