Exception Type: Nil Object Exception

1: Function ObjectListbox.SetEditColumnsList( Listbox ) as boolean
2: Sub MainWindow.MainWindow.EditListColumns( MainWindow.MainWindow )
3: Function MainWindow.MainWindow._EditColumns_Action( MainWindow.MainWindow ) as boolean

User description of above error trace:

Tried simply to reorganize and rearrange the Edit→List Columns, when I got this bug.

Fixed.