Sorry the "external" workbook will be on the same machine but will be in a different folder to the report workbook.
Are you asking me that sumproduct can work while internal workbook is closed? Or are you telling me that sumproduct can work while internal workbook is closed?

So I have a report workbook (reportemp.xlsx) which has the sumproduct formula which I would like to gather the data from incidentemp.xlsx, these workbooks will be stored in different location but on the same PC hard drive.