Just a tip, if you are using IBOutlets and seperate nib files, if you get a strange error like this:

*** Terminating app due to uncaught exception ‘NSUnknownKeyException’, reason: ‘[<UIViewController 0x44e8b0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key viewA.’

Check that the controller class is set correctly for both the Controller in the main file, and the File Owner in the Nib file you are referencing.

This error seems to happen when you link a nib file to a controller in IB, and the class types do not match. Strangley the error only happens when you link an IBOutlet inside that controller though!

This thread describes the problem and solution a little:

http://forums.macrumors.com/archive/index.php/t-576991.html