Insert key on keyboard for Macbook Air Mountain Lion OS
An external keyboard or on screen keyboard with numpad is required.

See page 4 here > http://na.sage.com/sage-300-erp/sage-300-erp-online/~/media/site/sage-300-erp/assets/online/Sage-300-ERP-Online-Mac-Resource-Guide.pdf

Mac keyboards lack the Insert key which is used in Sage 300 ERP for adding new lines to lists.

So instead, if using a Mac, on a keyboard with a number pad, with Numlock OFF, the “0” button will act as the Insert key.