Ahah, very useful! So the app fails to load a dynamic library in a framework called CalendarStore and this appears to be a feature of Leopard (OS X 10.5). Although iSale 5 is supposed to support OS X 10.4 as well (see
this anouncement) I wonder if it in fact requires a feature only available in Leopard. I say that because on searching Google for "/System/Library/Frameworks/CalendarStore.framework" all of the links (well the ones I looked at anyway) were talking about OS X 10.5.