Saving Data Over Time

I have created a game were there is multiple levels and it has a menu were all the levels are listed. After one completes the level, i want the level to stay unlocked even when they exit the app. I have used an attribute to define when a level should be unlocked. When one completes a level it adds one to the attribute unlocking the next level. I have used save attribute but when i exit the app and take it off the multitasking bar (im on an iPod Touch 4th gen) all the levels are locked again. can anyone help me keep the levels unlocked at all times once they are completed???
Comments
youll be good to go then
and tshirt looks like you owe me a pint now