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.
try fn+enter. Don't you hate it when you ask how to do something and people answer "why would you want to do that?"