Working with Start and End Dates

You must set the end date to be after the start date, for both the planned as well as actual dates, or else you will receive an error.

Both the start and end dates you specify for a task must fall within the axis dates, that is, the dates specified by the AxisEndDateTime and AxisStartDateTime properties. If you specify task dates that fall outside of the axis dates, the task appears in the table section of the Gantt chart, but no bar appears in the chart section of the Gantt chart, even if one of the dates falls inside the axis dates.