Unable to select objects on screen or unable to draw on screen

The inability to select objects on screen or to draw on screen is usually caused by a zero-length or zero-width element having been drawn. While in mouse selection mode, click on an element drawn on the screen to select it. If selection is not possible, a zero-length element is likely selected, so press the Delete key (Del on the keyboard or the Delete button in the program interface) to remove the faulty element. Continue left-clicking and then pressing the Del (Delete) key until the element you click on becomes selectable. If necessary, continue the process on other storeys where the problem exists. Once selection with the mouse in selection mode is achieved, the problem is resolved.