When does below error occur?

The GridView 'grid_view_employee_details' fired event RowDeleting which wasn't handled.

Answer:

When we did not handle grid_view_employee_details_RowDeleting event in code-behind, and wrote delete functionality inside other event i.e. grid_view_employee_details_RowCommand event, then "The GridView 'grid_view_employee_details' fired event RowDeleting which wasn't handled." error occurs.

So for working with this event, we have to create an empty
row_deleting event as

protected void grid_view_employee_details_RowDeleting(object sender, GridViewDeleteEventArgs e)

{

      //do not write any code

}

By handling this event, error will never come.