MKErrorDomain error 4 iPhone

I keep getting this randomly when I run my gps app I'm building. It doesn't happen everytime, and the coordinates passed in are always valid (i nslog them). Is there documentation for these somewhere?

EDIT:

CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(locManager.location.coordinate.latitude, locManager.location.coordinate.longitude);
geocoder1 = [[MKReverseGeocoder alloc] initWithCoordinate:coord];
geocoder1.delegate = self;
[geocoder1 start];

and then about half the time it returns an error. I tried releasing and re-assigning the geocoder if there was an error, but that didn't help. Only thing that did was restarting the app.

Solution

I've been hitting this error repeatedly, and was unable to figure out how to make it stop; but I finally found an end-run around the whole issue that works quite well, and only takes a little more work: Don't use Apple's MKReverseGeocoder at all -- instead, directly call Google's reverse-geocoding API (this is apparently the same service that MKReverseGeocoder does behind the scenes). You can get back either JSON or XML (your preference), which you will then have to parse, but that isn't too hard.

For example, since my app is using ASIHTTPRequest, this is what it looks like (although this would also be easy to do with do with Apple's native APIs such as NSURLConnection):

#pragma mark -
#pragma mark CLLocationManagerDelegate

- (void)locationManager:(CLLocationManager *)manager 
    didUpdateToLocation:(CLLocation *)newLocation 
           fromLocation:(CLLocation *)oldLocation
{
    // Be careful: My code is passing sensor=true, because I got the lat/long
    // from the iPhone's location services, but if you are passing in a lat/long
    // that was obtained by some other means, you must pass sensor=false.
    NSString* urlStr = [NSString stringWithFormat:
      @"http://maps.googleapis.com/maps/api/geocode/xml?latlng=%f,%f&sensor=true",
      newLocation.coordinate.latitude, newLocation.coordinate.longitude];
    NSURL* url = [NSURL URLWithString:urlStr];
    self.reverseGeocoderRequest = [ASIHTTPRequest requestWithURL:url];
    self.reverseGeocoderRequest.delegate = self;
    [self.reverseGeocoderRequest startAsynchronous];
}

By the way, Google's API has rules, just like Apple's does. Make sure you read the docs, especially regarding quotas.