CoreLocation kCLErrorDomain error 5

It also happens if you:

stop monitoring a region

[self.manager stopMonitoringForRegion:region];

and request the state for all monitored regions shortly afterwards:

for (CLRegion *region in self.manager.monitoredRegions) {
    [self.manager requestStateForRegion:region];
}

you will get the kCLErrorDomain 5 because IOS seems to have disabled the monitoring for that region, but has not yet removed it from the monitoredRegions array

monitoringDidFailForRegion CLCircularRegion (identifier:'Home', center:<...>, radius:102.00m) The operation couldn’t be completed. (kCLErrorDomain error 5.)
monitoredRegion: CLCircularRegion (identifier:'Home', center:<...>, radius:102.00m)
monitoredRegion: CLBeaconRegion (identifier:'BeaconHome', uuid:<..., major:(null), minor:(null))
monitoredRegion: CLCircularRegion (identifier:'D...', center:<...>, radius:101.00m)
monitoredRegion: CLCircularRegion (identifier:'W...', center:<..>, radius:51.00m)

to work around that problem, do something like this:

- (void)locationManager:(CLLocationManager *)manager monitoringDidFailForRegion:(CLRegion *)region withError:(NSError *)error
{
    NSLog(@"monitoringDidFailForRegion %@ %@",region, error.localizedDescription);
    for (CLRegion *monitoredRegion in manager.monitoredRegions) {
        NSLog(@"monitoredRegion: %@", monitoredRegion);
    }
    if ((error.domain != kCLErrorDomain || error.code != 5) &&
        [manager.monitoredRegions containsObject:region]) {
        NSString *message = [NSString stringWithFormat:@"%@ %@",
            region, error.localizedDescription];
        [AlertView alert:@"monitoringDidFailForRegion" message:message];
    }
}

Also: if you're testing with iBeacons, you can't use the iOS simulator.

I hate to answer my own question, but I have found the solution to my issue. A kCLErrorDomain code/error of 5 denotes that you have tried to monitor more than 20 CLRegions. In my case, both subclasses were guilty of monitoring more than 20 regions.

It is also possible to get this error code back when your latitude and longitude values don't make sense. (I'd transposed them, for example, and was vexed by this error for a while.)