Columns.SortColumns array is a readonly array.
To change this array you should change .SortOrder of some column, for example:
[list]
if you change SortOrder from None to Ascending from certain column, this column will inserted into Columns.SortColumns array.[/*:m]
if you change SortOrder from Ascending to None from certain column, this column will deleted Columns.SortColumns array.[/*:m][/list:u]