It sounds like pictures which can no longer be found.
E.g. if you copy-paste a picture from Word in your webpage, it will look OK until you publish the page - then picture disappears and you see these boxes. The right way to insert a picture is load it on our Server - click on Picture button in editor toolbar while editing a page.
To delete these boxes, select them and click Delete.
Dmitry Buterin, Chief Apricot