Area select does not function on background pages

[Tony B]

Does anyone have a suggested resolution for why the area or lasso select functions do not work on background pages (only)?

[Paul Herber]

It does work, but only when the background page is the active page. Also, the shapes may have been made non-selectable.
Also, shapes may not select if their whole area is not included within the selection.
Can you select the shapes individually?
Options -> General -> Select shapes partially within area