I have developed an application that will hold the lessons of each day of the week. On the right tableview, the user creates a day, then he/she creates the lessons for this day and sets the assignment for this day. I have done the application in Cocoa bindings for the first time, and I have some problems with saving-loading. This is what I have done so far When I create some information on the 2 tableviews, all is fine. When I save them and try to load them, nothing is being changed, and when I try to create some more days and lessons, there is an "invisible" day allocated, that can be pressed but cannot be edited. Nothing more is loaded properly. Any ideas of what may be wrong? PS. The application is in testing stage: There are some really obvious mistakes. However, think that the solution to my problem is really simple, only I cannot see it! Any help would be appreciated.