Invalid Region error only on one device - ios

Question

I'm trying to show a map in my application, it works on my simulator and on my ipod touch 4g.
But I always get an error on my iPhone and I don't know why this happens.
Maybe you can explain me why it fails.
The error is:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Invalid Region <center:nan, nan span:nan, nan>'
I already searched for solutions on google and stackoverflow but it seems that nobody has this problem.
Thats my code:
//setup mapview
mapView.delegate = self;
mapView.showsUserLocation = YES;
//set up core location
locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
//Set up zoom location
CLLocationCoordinate2D zoomLocation;
zoomLocation.latitude = locationManager.location.coordinate.latitude;
zoomLocation.longitude= locationManager.location.coordinate.longitude;
debug(#"Location: %f und %f",locationManager.location.coordinate.latitude,locationManager.location.coordinate.longitude);
//zoom to location
MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, 0.5*METERS_PER_MILE, 0.5*METERS_PER_MILE);
MKCoordinateRegion adjustedRegion = [mapView regionThatFits:viewRegion];
[mapView setRegion:adjustedRegion animated:YES];
As I said, it works on iPod and simulator, but not on iPhone.
Hope you can help me
SOLUTION:
I used the locationManager too early, so the app crashed. Now I used it this way:
- (void)viewDidLoad {
[super viewDidLoad];
//setup mapview
mapView.delegate = self;
mapView.showsUserLocation = YES;
//set up core location
locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
[locationManager startUpdatingLocation];
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation{
//Set up zoom location
CLLocationCoordinate2D zoomLocation;
zoomLocation.latitude = newLocation.coordinate.latitude;
zoomLocation.longitude= newLocation.coordinate.longitude;
MKCoordinateRegion viewRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, 0.5*METERS_PER_MILE, 0.5*METERS_PER_MILE);
MKCoordinateRegion adjustedRegion = [mapView regionThatFits:viewRegion];
[mapView setRegion:adjustedRegion animated:YES];
debug(#"Location: %f und %f",newLocation.coordinate.latitude,newLocation.coordinate.longitude);
}
Don't know if this way is 100% correct, but it works.