schedule data refresh issue

I have set up some web parts that show excel graphs based on power pivot data. the data is drawn in from sharepoint online and i get it into excel using an odata feed connection. i cannot set up a scheduled refresh of the data? it give an error

ExcelServices operation ended with errors: ExternalDataRefreshFailed: An error occurred while working on the Data Model in the workbook. Please try again. Correlation ID: 67a5213f-3c00-4fef-898b-a313a6ff856f

i do not have a personal gateway installed. why should this be an issue as the data is from sharepoint online and the workbook is on shrepoint online?