ALAssetsLibraryWriteVideoCompletionBlock return undefined values

ALAssetsLibraryWriteVideoCompletionBlock is returning undefined values. If assetURL is equal to nil, then error ought to be not equal to nil, that is, return to me some error description.

See apple documentation at here.

When I record small video, ALAssetsLibraryWriteVideoCompletionBlock return a good value of assetURL, but when I record long video 3 or 4 Gb, assetURL return nil and error return nil. Video recorded is in tmp file because I can see this video in temporally folder in my app. It seems like IOS framework try to do a copy of this temporally file to photo album and iPhone don't have enough memory to copy this temp file to photo album and return a path of this file (assetURL).

Is this a bug in iOS framework? If so, is there a way to fix it?

UPDATE: My files is less than 4GB. Thanks

UPDATE with source code:

    -(void)recorder:(AVCamRecorder *)recorder recordingDidFinishToOutputFileURL:(NSURL *)outputFileURL error:(NSError *)error
    {    
    if ([[self recorder] recordsAudio] && ![[self recorder] recordsVideo]) {
    // If the file was created on a device that doesn't support video recording, it can't be saved to the assets 
    // library. Instead, save it in the app's Documents directory, whence it can be copied from the device via
    // iTunes file sharing.
    [self copyFileToDocuments:outputFileURL];

    if ([[UIDevice currentDevice] isMultitaskingSupported]) {
        [[UIApplication sharedApplication] endBackgroundTask:[self backgroundRecordingID]];
    }       

    if ([[self delegate] respondsToSelector:@selector(captureManagerRecordingFinished:)]) {
        [[self delegate] captureManagerRecordingFinished:self];
    }
}
else {  
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    [library writeVideoAtPathToSavedPhotosAlbum:outputFileURL
                                completionBlock:^(NSURL *assetURL, NSError *error) {
                                    if (error) {
                                        if ([[self delegate] respondsToSelector:@selector(captureManager:didFailWithError:)]) {
                                            [[self delegate] captureManager:self didFailWithError:error];
                                        }                                           
                                    }

                                    if ([[UIDevice currentDevice] isMultitaskingSupported]) {
                                        [[UIApplication sharedApplication] endBackgroundTask:[self backgroundRecordingID]];
                                    }

                                    if (assetURL!=nil)
                                    {
                                        if ([[self delegate] respondsToSelector:@selector(captureManagerRecordingFinished:)]) {
                                        [[self delegate] captureManagerRecordingFinished:self];
                                        }
                                    }
                                    else
                                    {
                                        NSLog(@"Video is not saved");
                                        NSString *alertMsg = [NSString stringWithFormat:@"Impossible to copy video to photo album"];
                                        UIAlertView *alert = [[UIAlertView alloc] init];
                                        [alert setTitle:@"info"];
                                        [alert setMessage:alertMsg];
                                        [alert setDelegate:self];
                                        [alert addButtonWithTitle:@"Accept"];
                                        [alert show];
                                    }
                                }];
     }
}