Removing annotations from my map view in the following way:

```
 if ([[self.mapView annotations] count] > 0)
{
    [self.mapView removeAnnotations:[self.mapView annotations]];
}

```

causes my application to crash with the following exception:

```
*** Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <MKAnnotationContainerView 0xe87b420> for the key path "title" from <PFAnnotation 0x10851230> because it is not registered as an observer.'

```

The annotations are added in the following way:

```
 CLLocationCoordinate2D pinPosition;
for (int index = 0; index < [array count]; index++)
{        
    Station *aStation = [array objectAtIndex:index];
    PFAnnotation *stationPin = [[PFAnnotation alloc] init]; //StationPinView
    pinPosition = CLLocationCoordinate2DMake([[aStation valueForKey:@"latitude"] doubleValue], [[aStation valueForKey:@"longitude"] doubleValue]);
    stationPin.stationName = [aStation valueForKey:@"stationName"];
    stationPin.stationPosition = pinPosition;
    stationPin.stationLength = [aStation valueForKey:@"platformLength"];

    [self.mapView addAnnotation:stationPin];
    [stationPin release];        

}

```

My PFAnnotation.h is:

```
@interface PFAnnotation : NSObject <MKAnnotation>
{
    NSString *stationName;
    CLLocationCoordinate2D stationPosition;
    NSNumber *stationLength;

}

@property (nonatomic, retain) NSString *stationName;
@property CLLocationCoordinate2D stationPosition;
@property (nonatomic, retain) NSNumber *stationLength;

@end

```

and my PFAnnotation.m is:

```
@implementation PFAnnotation

@synthesize stationName;
@synthesize stationPosition;
@synthesize stationLength;

- (CLLocationCoordinate2D)coordinate;
{
    return stationPosition; 
}

- (NSString *)title
{
    return stationName;

}

- (NSString *)subtitle
{
    if (stationLength == nil)
        return nil;
    else
        return [NSString stringWithFormat:@"Platform Length: %@ft",stationLength];
}

- (void)dealloc {
    [stationName release];
    [stationLength release];
    [super dealloc];
}

```

I have read in some other threads that, setting the annotation properties from background thread is the reason for the above error. But in my case,it is not so because every thing is performed on the main thread. Please advise.