In the past, Sage always recommended using .csv. We had users use .xls in some cases. It seemed the jobs would work for a period of time, sometimes years, and then all of a sudden not work with nothing changing. The workaround was always to redesign it using .csv instead. That always did the trick so I always use and recommend that. Maybe .xls or .xlsx works better with the newer versions of both Excel and Sage, but as long as .csv works, that's my go to.