Creating an iPhone Application in Xcode 4.1.1 - Program received signal "SIGABRT" - iphone

Question

I'm new to creating iPhone Applications and have just started with Xcode and am getting the following errors; I have used this code previously on both the simulator & an iPod touch and it worked fine for both but for some reason lately it will not allow me to go from one page to another without giving me the "SIGABRT" error.
Basically in my application I need to go from one page to another several times but it will not work....can anyone help with this please?
This is the code it seems unhappy with (it complies & builds successfully):
1 #import <UIKit/UIKit.h>
2
3 int main(int argc, char *argv[])
4 {
5 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
6 int retVal = UIApplicationMain(argc, argv, nil, nil);
7 [pool release];
8 return retVal;
9 }
It stops on the int retVal line (6th line).
When debugging it gave the error:
2011-09-09 15:33:59.029 TruckFile[1072:b603] * Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[< UIApplication 0x6044600> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key window.'
Can anyone help me with this please?
Thank you in advance!
========================================
Code files:
========================================
Main page (.h)
#import <UIKit/UIKit.h>
#import "ViewTwoController.h"
#import "TruckFileAppDelegate.h"
#interface TruckFileAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *window;
ViewTwoController *viewTwoContoller;
UINavigationController *navigationController;
}
#property (nonatomic, retain) IBOutlet UIWindow *window;
#property (nonatomic, retain) IBOutlet UINavigationController *navigationController;
#property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
#property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
#property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
#property (nonatomic, retain) ViewTwoController *viewTwoController;
-(IBAction)switchPage:(id)sender;
#end
================================================
Main page (.m)
#import "TruckFileAppDelegate.h"
#import "ViewTwoController.h"
#implementation TruckFileAppDelegate
#synthesize window;
#synthesize navigationController;
#synthesize managedObjectContext = __managedObjectContext;
#synthesize managedObjectModel = __managedObjectModel;
#synthesize persistentStoreCoordinator = __persistentStoreCoordinator;
#synthesize viewTwoController;
-(IBAction)switchPage:(id)sender
{
if(self.viewTwoController == nil)
{
ViewTwoController *viewTwo = [[ViewTwoController alloc]
initWithNibName:#"ViewTwoController" bundle:[NSBundle mainBundle]];
self.viewTwoController = viewTwo;
[viewTwo release];
}
[self.navigationController pushViewController:self.viewTwoController animated:YES];
}
- (void)dealloc {
[navigationController release];
[window release];
[super dealloc];
}
#end
====================================
Page 2 (.h)
#import <UIKit/UIKit.h>
#interface ViewTwoController : UIViewController {
}
#end
=====================================
Page 2 (.m)
#import "ViewTwoController.h"
#implementation ViewTwoController
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning]; // Releases the view if it doesn't have a superview
// Release anything that's not essential, such as cached data
}
- (void)dealloc {
[super dealloc];
}
#end

Answer 1

The mainWindow.xib is trying to connect it's UIWindow instance with your UIApplicationDelegate's and it can't find it (that's why it complains it can't set the value for an UNDEFINED key).
Check your UIApplicationDelegate class has a UIWindow iVar, a property in its .h and it's correctly synthesized in its .m.
EDIT
Who's calling the method switchPage: on UIApplication? If you are, you're calling it on the wrong object. Instead of doing
[[UIApplication sharedApplication] switchPage:xxx];
You should do:
[[[UIApplication sharedApplication] delegate] switchPage:xxx];
Since the method switchPage: is defined in the UIApplicationDelegate class.

Answer 2

Your code fails at
[UIApplication switchPage:]:

Answer 3

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIApplication switchPage:]: unrecognized selector sent to instance 0x600beb0'
This means that in your switchPage method, you are giving an action to an unknown identifier, maybe check the object identifier name, and check if you have initialized it in your .h file.