1 the user schedules has issues with the DB data access
-Had try schedule other report, all running fine therefore should be no issue with DB data access.
2 There was a ETL refresh and the source table was truncated when the report was scheduled
-There is no ETL refresh in the background.
3 there are some prompt values in the schedule that return no values. Check if all the prompts are proper.
-Is it posibble that prompt value in schedule return no values but return value in when manually refresh?